Stock-Based Compensation - Option Activity under Principal Option Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares, Beginning Balance	184,000	83,000
Shares, Granted	0	101,000	0
Shares, Exercised	(58,000)	0
Shares, Forfeited	0	0
Shares, Expired	0	0
Shares, Ending Balance	126,000	184,000	83,000
Weighted Average Exercise Price, Beginning Balance	$ 19.71	$ 11.99
Shares, Exercisable	28,000
Weighted Average Exercise Price, Granted		26.02
Weighted Average Exercise Price, Exercised	$ 12.02
Weighted Average Exercise Price, Forfeited	0	0
Weighted Average Exercise Price, Expired	0	0
Weighted Average Exercise Price, Ending Balance	$ 23.23	$ 19.71	$ 11.99
Aggregate Intrinsic Value, Beginning Balance	$ 3,540	$ 1,247
Weighted Average Exercise Price, Exercisable	$ 13.36
Aggregate Intrinsic Value, Ending Balance	$ 1,088	$ 3,540	$ 1,247
Weighted-Average Remaining Contractual Term, Outstanding	3 years 2 months 27 days	3 years 7 months 2 days	3 years 3 months 11 days
Aggregate Intrinsic Value, Exercisable	$ 523
Weighted-Average Remaining Contractual Term, Exercisable	2 years 3 months 22 days