Reconciliation of Basic and Diluted Earnings Per Share Computations (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Earnings Per Share Disclosure [Line Items]
Net income	$ 14,333	$ 21,286	$ 13,937	$ 13,910	$ 28,044	$ 12,915	$ 14,899	$ 7,904	$ 63,466	$ 63,762	$ 25,597
Basic weighted average shares									14,133,925	14,052,311	14,980,429
Effect of common stock equivalents:
Assumed exercise of stock options and vesting of stock grants									211,628	275,509	202,856
Diluted weighted average shares									14,345,553	14,327,820	15,183,285
Net income per common share:
Basic	$ 1.01	$ 1.50	$ 0.99	$ 0.99	$ 2.00	$ 0.92	$ 1.06	$ 0.57	$ 4.49	$ 4.54	$ 1.71
Diluted	$ 1.00	$ 1.48	$ 0.97	$ 0.97	$ 1.96	$ 0.90	$ 1.05	$ 0.56	$ 4.42	$ 4.45	$ 1.69