Summary of Stock Option Activity (Parenthetical) (Detail) - shares		3 Months Ended
		Mar. 31, 2018		Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units	[2]	721,581	[1]	729,017
Exercisable amount of stock appreciation right units	[2],[3]	527,310
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units		656,498
Exercisable amount of stock appreciation right units		475,608
Stock Appreciation Rights (SARs) | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of stock appreciation right units		75.00%

[1] Due to the ceiling imposed on the SAR grants, the outstanding amount equals a maximum of 656,498 shares of the Company's common stock issuable upon exercise.

[2] The SAR units are convertible for a maximum number of shares of the Company's common stock equal to 75% of the SAR units subject to the grant.

[3] Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 475,608 shares of the Company's common stock issuable upon exercise.