Income Per Common Share (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Numerator:
Net income	$ 6,708	$ 6,306	$ 47,044	$ 55,854
Total dividends on preferred stocks			(300)	(305)
Numerator for basic net income per common share - net income applicable to common stock	6,708	6,306	46,744	55,549
Dividends on preferred stocks assumed to be converted, if dilutive			300	305
Interest expense including amortization of debt issuance costs, net of income taxes, on convertible debt assumed to be converted, if dilutive		8		298
Numerator for diluted net income per common share	6,708	6,314	47,044	56,152
Denominator:
Denominator for basic net income per common share - weighted-average shares	22,374	22,241	22,346	21,851
Effective of dilutive securities:
Convertible preferred stocks	916,666	935,366	917,119	935,540
Stock options	261,341	317,420	264,965	345,245
Convertible notes payable		32,391		366,894
Dilutive potential common shares	1,178,007	1,285,177	1,182,084	1,647,679
Denominator for diluted net income per common share - adjusted weighted-average shares and assumed conversions	23,552	23,526	23,528	23,499
Basic net income per common share	$ 0.30	$ 0.28	$ 2.09	$ 2.54
Diluted net income per common share	$ 0.28	$ 0.27	$ 2.00	$ 2.39
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)
Noncumulative Preferred Stock [Member]
Numerator:
Total dividends on preferred stocks				$ (5)