Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 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	66,000	[1]
Number of shares, Options/SAR units exercised | shares	(940,526)	[1]
Number of shares, Options/SAR units forfeited or expired | shares	(37,633)	[1]
Number of shares outstanding, Ending balance | shares	1,494,296	[1],[2]
Number of shares exercisable, Ending balance | shares	981,117	[1],[3]
Weighted-average exercise price
Weighted-average exercise price, Beginning balance | $ / shares	$ 18.15
Weighted average exercise price, Granted | $ / shares	27.17
Weighted average exercise price, Exercised | $ / shares	16.76
Weighted average exercise price, Forfeited or expired | $ / shares	17.89
Weighted average exercise price, Ending balance | $ / shares	19.42	[2]
Weighted average exercise price, exercisable | $ / shares	$ 19.97	[3]
Weighted average remaining contractual term
Weighted average remaining contractual life, Outstanding at end of period	4 years 9 months 18 days	[2]
Weighted average remaining contractual life, Exercisable at end of period	4 years	[3]
Aggregate intrinsic value
Aggregate intrinsic value, Outstanding | $	$ 23,378,563	[2]
Aggregate intrinsic value, Exercisable | $	$ 14,809,518	[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 1,331,360 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 895,288 shares of the Company's common stock issuable upon exercise.