Income Per Common Share - Computation of Basic and Diluted Net Income Per Common Share (Detail) (USD $) In Thousands, except 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	$ 11,113	$ 7,427	$ 22,754	$ 7,359
Total dividends on preferred stocks			(300)	(300)
Numerator for basic net income per common share-net income applicable to common stock	11,113	7,427	22,454	7,059
Dividends on preferred stocks assumed to be converted, if dilutive			300	60
Numerator for diluted net income per common share	11,113	7,427	22,754	7,119
Denominator:
Denominator for basic net income per common share-weighted-average shares	22,544,857	22,437,485	22,538,773	22,430,589
Effect of dilutive securities:
Convertible preferred stocks	916,666	916,666	916,666	250,000
Stock options	198,715	223,232	195,000	234,071
Dilutive potential common shares	1,115,381	1,139,898	1,111,666	484,071
Denominator for diluted net income per common share-adjusted weighted-average shares and assumed conversions	23,660,238	23,577,383	23,650,439	22,914,660
Basic net income per common share	$ 0.49	$ 0.33	$ 1.00	$ 0.31
Diluted net income per common share	$ 0.47	$ 0.31	$ 0.96	$ 0.31
Series B Preferred Stock [Member]
Numerator:
Total dividends on preferred stocks			(240)	(240)
Series D Preferred Stock [Member]
Numerator:
Total dividends on preferred stocks			$ (60)	$ (60)