Summary of Stock Option Activity (Parenthetical) (Detail) - shares		6 Months Ended
		Jun. 30, 2017		Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units	[2]	870,874	[1]	1,455,908
Exercisable amount of stock appreciation right units	[2],[3]	565,168
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units		790,118
Exercisable amount of stock appreciation right units		515,026
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 790,118 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 515,026 shares of the Company's common stock issuable upon exercise.