Subsequent Events - Pro Forma Share and Per Share Data, Giving Retroactive Effect to the Stock Split (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Weighted average shares outstanding:
Basic weighted average shares outstanding, as reported (pre-stock split)	16,564,338	16,883,111
Diluted weighted average shares outstanding, as reported (pre-stock split)	16,799,719	17,280,445
Earnings per common share:
Basic earnings per share, as reported (pre-stock split)	$ 0.74	$ 1.28
Diluted earnings per share, as reported (pre-stock split)	$ 0.73	$ 1.25
Subsequent Event [Member]
Weighted average shares outstanding:
Basic weighted average shares outstanding, pro forma (post-stock split)	33,128,676	33,766,222
Diluted weighted average shares outstanding, pro forma (post-stock split)	33,599,438	34,560,890
Earnings per common share:
Basic earnings per share, pro forma (post-stock split)	$ 0.37	$ 0.64
Diluted earnings per share, pro forma (post-stock split)	$ 0.37	$ 0.62