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, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Numerator:
Net income allocable to common stockholders	$ 12,725	$ 10,299	$ 29,636	$ 19,347
Denominator:
Denominator for basic earnings per share - weighted average shares	8,915	8,802	8,910	8,792
Effect of dilutive employee stock options and warrants	228	95	230	89
Denominator for diluted earnings per share - adjusted weighted average shares and assumed exercise	9,143	8,897	9,140	8,881
Basic:
Net income allocable to common stockholders	$ 1.43	$ 1.17	$ 3.33	$ 2.20
Diluted:
Net income allocable to common stockholders	$ 1.39	$ 1.16	$ 3.24	$ 2.18
Outstanding common stock equivalents having no dilutive effect	44	548	44	637