Stock-Based Compensation - Option Activity under Principal Option Plans (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Shares, Beginning Balance	184,000
Shares, Granted	0
Shares, Exercised	0	0
Shares, Forfeited	0
Shares, Expired	0
Shares, Ending Balance	184,000		184,000
Shares, Exercisable	86,000
Weighted Average Exercise Price, Beginning Balance	$ 19.71
Weighted Average Exercise Price, Granted	$ 0
Weighted Average Exercise Price, Exercised	$ 0
Weighted Average Exercise Price, Forfeited	$ 0
Weighted Average Exercise Price, Expired	$ 0
Weighted Average Exercise Price, Ending Balance	$ 19.71		$ 19.71
Weighted Average Exercise Price, Exercisable	$ 12.46
Weighted-Average Remaining Contractual Term, Outstanding	3 years 4 months 6 days		3 years 7 months 2 days
Weighted-Average Remaining Contractual Term, Exercisable	2 years 3 months 18 days
Aggregate Intrinsic Value, Beginning Balance	$ 3,540
Aggregate Intrinsic Value, Ending Balance	4,017		3,540
Aggregate Intrinsic Value, Exercisable	$ 2,505