Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016 USD ($) $ / shares shares
Number of options and SAR units
Number of shares outstanding, Beginning balance | shares	2,406,455	[1]
Number of shares, Options/SAR units granted | shares	0	[1]
Number of shares, Options/SAR units exercised | shares	(31,263)	[1]
Number of shares, Options/SAR units forfeited or expired | shares	(18,872)	[1]
Number of shares outstanding, Ending balance | shares	2,356,320	[1],[2]
Number of shares exercisable, Ending balance | shares	1,619,955	[1],[3]
Weighted-average exercise price
Weighted-average exercise price, Beginning balance | $ / shares	$ 18.15
Weighted average exercise price, Granted | $ / shares	0
Weighted average exercise price, Exercised | $ / shares	10.29
Weighted average exercise price, Forfeited or expired | $ / shares	17.41
Weighted average exercise price, Ending balance | $ / shares	18.26	[2]
Weighted average exercise price, exercisable | $ / shares	$ 18.84	[3]
Weighted average remaining contractual term
Weighted average remaining contractual life, Outstanding at end of period	4 years 2 months 12 days	[2]
Weighted average remaining contractual life, Exercisable at end of period	3 years 4 months 24 days	[3]
Aggregate intrinsic value
Aggregate intrinsic value, Outstanding | $	$ 11,897,435	[2]
Aggregate intrinsic value, Exercisable | $	$ 7,773,094	[3]

[1] 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.

[2] Due to the ceiling imposed on the SAR grants, the outstanding amount equals a maximum of 2,064,112 shares of the Company's common stock issuable upon exercise.

[3] Due to the ceiling imposed on the SAR grants, the exercisable amount equals a maximum of 1,450,567 shares of the Company's common stock issuable upon exercise.