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Stock-Based Compensation - Additional Information (Detail)
In Millions, except Share data, unless otherwise specified |
12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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Mar. 31, 2013
USD ($)
|
Mar. 31, 2013
AUD
|
Mar. 31, 2012
USD ($)
|
Mar. 31, 2012
AUD
|
Mar. 31, 2011
USD ($)
|
Mar. 31, 2011
AUD
|
Sep. 14, 2012
Restricted Stock Units Performance Vesting [Member]
|
Jun. 30, 2012
Restricted Stock Units Performance Vesting [Member]
|
Jun. 07, 2012
Restricted Stock Units Performance Vesting [Member]
|
Jun. 07, 2011
Restricted Stock Units Performance Vesting [Member]
|
Mar. 31, 2013
Restricted Stock Units Performance Vesting [Member]
|
Sep. 14, 2012
Restricted stock units (market condition) [Member]
|
Dec. 17, 2011
Restricted stock units (market condition) [Member]
|
Sep. 15, 2011
Restricted stock units (market condition) [Member]
|
Jun. 21, 2012
Long Term Incentive Award [Member]
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Jun. 21, 2012
Long Term Incentive Award [Member]
Maximum [Member]
|
Dec. 07, 2012
Restricted stock units service vesting [Member]
|
Dec. 17, 2011
Restricted stock units service vesting [Member]
|
Dec. 07, 2011
Restricted stock units service vesting [Member]
|
May 30, 2011
Restricted stock units service vesting [Member]
|
Mar. 31, 2013
2001 Equity Incentive Plan [Member]
|
Mar. 31, 2012
2001 Equity Incentive Plan [Member]
|
Aug. 31, 2007
Long-Term Incentive Plan [Member]
|
Nov. 30, 2006
Long-Term Incentive Plan [Member]
|
Mar. 31, 2013
Long-Term Incentive Plan [Member]
|
|
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||||||||||||||||||||||||
| Stock-based compensation expense | $ 10.8 | $ 11.1 | $ 11.3 | ||||||||||||||||||||||
| Compensation expense related to equity-based awards | 7.0 | 7.8 | 9.1 | ||||||||||||||||||||||
| Compensation expense related to liability-classified awards | 3.8 | 3.3 | 2.2 | ||||||||||||||||||||||
| Unrecognized compensation cost related to stock-based compensation cost | 11.3 | ||||||||||||||||||||||||
| Estimated weighted average amortisation, period of recognition | 1 year 6 months | 1 year 6 months | |||||||||||||||||||||||
| Issue of shares authorised | 45,077,100 | ||||||||||||||||||||||||
| Percentage of options exercised after first year | 25.00% | ||||||||||||||||||||||||
| Percentage of options exercised after second year | 25.00% | ||||||||||||||||||||||||
| Percentage of options exercised after third year | 50.00% | ||||||||||||||||||||||||
| Unexercised option expiration year | 10 years | 10 years | |||||||||||||||||||||||
| Unexercised options expiration days | 90 days | ||||||||||||||||||||||||
| Restricted stock units granted | 1,415,605 | 1,415,605 | 1,303,209 | 1,303,209 | 432,654 | 954,705 | 265,988 | 281,556 | 265,988 | 285,358 | |||||||||||||||
| Restricted stock units outstanding | 4,004,368 | 4,004,368 | 3,677,511 | 3,677,511 | 5,112,095 | 5,112,095 | 579,432 | 3,424,936 | |||||||||||||||||
| LTI units granted | 450,336 | 266,627 | 63,146 | 501,556 | 1,083,021 | 7,265,992 | |||||||||||||||||||
| Granted options | 1,016,000 | 1,132,000 | |||||||||||||||||||||||
| Options outstanding | 1,677,102 | ||||||||||||||||||||||||
| Intrinsic value of stock options exercised | 7.2 | 2.0 | 0.6 | ||||||||||||||||||||||
| Tax benefits from stock options exercised | $ 3.5 | $ 0.4 | |||||||||||||||||||||||
| Closing stock price | 10.01 | ||||||||||||||||||||||||
| Restricted stock units vested | 846,415 | 846,415 | 2,527,601 | 2,527,601 | 592,442 | 385,288 | 760,037 | 240,645 | 316,283 | 81,619 | 925,024 | ||||||||||||||
| Restricted stock unit deferred vesting period | 3 years | 2 years | |||||||||||||||||||||||
| Scorecard LTI - cash settled units granted under the terms of LTIP | 506,627 | 506,627 | 716,536 | 716,536 | |||||||||||||||||||||