Stock-Based Awards - Summary of Stock Options, Restricted Stock and Restricted Stock Unit Activity (Detail)	3 Months Ended
Mar. 31, 2019 shares
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options, beginning balance	570,537
Options, Granted	0
Options, Exercised/vested	(20,000)
Options, Forfeitures	0
Options, ending balance	550,537
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock, beginning balance	1,957,102
Restricted Stock, Granted	2,233,878
Restricted Stock, Exercised/vested	(827,721)
Restricted Stock, Forfeitures	(93,194)
Restricted Stock, ending balance	3,270,065
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock, beginning balance	9,494
Restricted Stock, Granted	35,283
Restricted Stock, Exercised/vested	(4,341)
Restricted Stock, Forfeitures	0
Restricted Stock, ending balance	40,436
Performance Based Restricted Stock Unites (PRSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted Stock, beginning balance	0
Restricted Stock, Granted	270,872
Restricted Stock, Exercised/vested	0
Restricted Stock, Forfeitures	0
Restricted Stock, ending balance	270,872

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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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).

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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.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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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.

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No definition available.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Number of share options (or share units) exercised during the current period.

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