Income Per Common Share - Computation of Basic and Diluted Net Income Per Share (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Numerator:
Net income:	$ 11,560	$ 6,708	$ 26,033	$ 14,303	$ 27,988	$ 6,306	$ 28,645	$ 20,903	$ 58,604	$ 83,842	$ 29,574
Total dividends on preferred stocks									(300)	(305)	(305)
Numerator for basic net income per common share-net income applicable to common stock	11,560	6,708	26,033	14,003	27,988	6,306	28,645	20,598	58,304	83,537	29,269
Dividends on preferred stocks assumed to be converted, if dilutive									300	305	305
Interest expense including amortization of debt issuance costs, net of income taxes, on convertible debt assumed to be converted, if dilutive										299	1,061
Numerator for diluted net income per common share									58,604	84,141	30,635
Denominator:
Denominator for basic net income per common share-weighted-average shares									22,359,967	21,962,294	21,168,184
Effect of dilutive securities:
Convertible preferred stocks									917,006	935,432	936,292
Stock options									261,596	325,752	186,258
Convertible notes payable										275,764	983,160
Dilutive potential common shares									1,178,602	1,536,948	2,105,710
Denominator for dilutive net income per common share-adjusted weighted-average shares and assumed conversions									23,538,569	23,499,242	23,273,894
Basic net income per common share	$ 0.52	$ 0.30	$ 1.17	$ 0.63	$ 1.26	$ 0.28	$ 1.29	$ 0.97	$ 2.61	$ 3.80	$ 1.38
Diluted net income per common share	$ 0.49	$ 0.28	$ 1.11	$ 0.61	$ 1.19	$ 0.27	$ 1.22	$ 0.90	$ 2.49	$ 3.58	$ 1.32
Series B Preferred Stock [Member]
Numerator:
Total dividends on preferred stocks									(240)	(240)	(240)
Series D Preferred Stock [Member]
Numerator:
Total dividends on preferred stocks									(60)	(60)	(60)
Noncumulative Preferred Stock [Member]
Numerator:
Total dividends on preferred stocks										$ (5)	$ (5)