Summary of Stock Option Activity (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, Granted	325,500
Outstanding amount of stock appreciation right units	3,316,380	[1]	3,115,972
Exercisable amount of stock appreciation right units	2,031,630	[2]
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding amount of stock appreciation right units	2,946,669
Exercisable amount of stock appreciation right units	1,894,343
Maximum | Stock Appreciation Rights (SARs)
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 2,946,669 shares of the Company's common stock issuable upon exercise.

[2] Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 1,894,343 shares of the Company's common stock issuable upon exercise.