Earnings Per Share - Computation of Basic and Diluted Earnings Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Numerator:
Net income allocable to common stockholders	$ 10,299	$ 6,638	$ 19,347	$ 12,390
Denominator:
Denominator for basic earnings per share-weighted average shares	8,802	8,706	8,792	8,696
Effect of dilutive employee stock options and warrants	95	72	89	75
Denominator for diluted earnings per share-adjusted weighted average shares and assumed exercise	8,897	8,778	8,881	8,771
Basic:
Net income allocable to common stockholders	$ 1.17	$ 0.76	$ 2.20	$ 1.42
Diluted:
Net income allocable to common stockholders	$ 1.16	$ 0.76	$ 2.18	$ 1.41
Outstanding common stock equivalents having no dilutive effect	548	536	637	536