Summary of Stock Option Activity (Parenthetical) (Detail) - shares		9 Months Ended
		Sep. 30, 2017		Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units	[2]	852,587	[1]	1,455,908
Exercisable amount of stock appreciation right units	[2],[3]	604,327
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units		775,403
Exercisable amount of stock appreciation right units		551,645
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 775,403 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 551,645 shares of the Company's common stock issuable upon exercise.