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Stock-Based Compensation - Additional Information (Detail) |  |  |  |  |  |  | 12 Months Ended
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Sep. 17, 2018 shares | Aug. 17, 2018 shares | Sep. 18, 2017 shares | Aug. 21, 2017 shares | Sep. 16, 2015 shares | Sep. 16, 2014 shares | Mar. 31, 2019 USD ($) shares | Mar. 31, 2019 AUD ($) shares | Mar. 31, 2018 USD ($) shares | Mar. 31, 2018 AUD ($) shares | Mar. 31, 2017 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Unrecognized compensation cost related to stock-based compensation cost | $ |  |  |  |  |  |  | $ 18,300,000 |  |  |  |
Estimated weighted average amortization, period of recognition |  |  |  |  |  |  | 2 years 2 months 24 days | 2 years 2 months 24 days |  |  |
Restricted stock units outstanding (in shares) |  |  |  |  |  |  | 4,261,508 |  | 4,137,592 | 4,137,592 | 3,340,245
Intrinsic value of stock options exercised | $ |  |  |  |  |  |  |  | $ 0 |  | $ 800,000 |
Excess tax benefits from share-based awards | $ |  |  |  |  |  |  | $ 0 |  | $ 0 |  | $ 3,000,000
Restricted stock units granted (in shares) |  |  |  |  |  |  | 1,714,094 | 1,714,094 | 1,779,904 | 1,779,904 |
Restricted stock units vested (in shares) |  |  |  |  |  |  | 745,787 | 745,787 | 615,334 | 615,334 |
Unvested restricted stock units cancelled (in shares) |  |  |  |  |  |  | 844,391 | 844,391 | 367,223 | 367,223 |
Scorecard LTI - cash settled units granted under the terms of LTIP (in shares) |  | 1,073,396 |  | 1,545,750 |  |  |  |  |  |  |
Average closing price period |  |  |  |  |  |  | 20 days | 20 days |  |  |
Restricted Stock Units Service Vesting [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Restricted stock units granted (in shares) |  |  |  |  |  |  | 617,793 | 617,793 | 332,262 | 332,262 |
Restricted stock units vested (in shares) |  |  |  |  |  |  | 242,964 | 242,964 | 237,480 | 237,480 |
Restricted Stock Units Performance Vesting [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
LTI units granted (in shares) |  | 357,797 |  | 515,249 |  |  |  |  |  |  |
Restricted stock units vested (in shares) |  |  |  |  |  |  | 284,350 | 284,350 |  |  |
Unvested restricted stock units cancelled (in shares) | 199,162 |  |  |  |  |  |  |  |  |  |
Restricted Stock Units (Market Condition) [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Restricted stock units granted (in shares) |  | 663,738 |  | 932,393 |  |  |  |  |  |  |
Restricted stock units vested (in shares) |  |  |  |  |  |  | 218,473 | 218,473 | 156,812 | 156,812 |
Long Term Incentive Award [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
LTI units granted (in shares) |  | 153,667 | 197,800 |  | 456,995 | 454,179 |  |  |  |  |
2001 Plan [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Issue of shares authorized (in shares) |  |  |  |  |  |  | 45,077,100 |  |  |  |
Percentage of grants exercised after first year (as percent) |  |  |  |  |  |  | 25.00% | 25.00% |  |  |
Percentage of grants exercised after second year (as percent) |  |  |  |  |  |  | 25.00% | 25.00% |  |  |
Percentage of grants exercised after third year (as percent) |  |  |  |  |  |  | 50.00% | 50.00% |  |  |
Restricted stock units outstanding (in shares) |  |  |  |  |  |  | 910,386 |  |  |  |
Long-Term Incentive Plan 2006 [Member] |  |  |  |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |  |  |  |
Restricted stock units outstanding (in shares) |  |  |  |  |  |  | 4,261,508 |  |  |  |
LTI units granted (in shares) |  |  |  |  |  |  | 13,571,439 | 13,571,439 |  |  |

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- Definition Total restricted stock units granted under the LTIP as of the balance sheet date. + References No definition available. + Details
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- Definition Unrecognized cost of unvested share-based compensation awards. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount of cash inflow from realized tax benefit related to deductible compensation cost reported on the entity's tax return for equity instruments in excess of the compensation cost for those instruments recognized for financial reporting purposes. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 20 -Section 55 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=109196918&loc=d3e11374-113907 + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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- Definition Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (d)(2) -URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901 + Details
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