Unaudited Interim Financial Data (Details) (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
Unaudited Interim Financial Data
Interest income	$ 28,584	$ 29,011	$ 29,225	$ 30,096	$ 31,229	$ 32,811	$ 33,873	$ 34,906	$ 116,916	$ 132,819	$ 156,183
Interest expense	2,955	3,466	3,951	4,398	4,751	5,084	6,032	6,559	14,770	22,426	39,032
Net interest income	25,629	25,545	25,274	25,698	26,478	27,727	27,841	28,347	102,146	110,393	117,151
Provision for loan losses	3,500	3,500	4,500	5,000	5,000	5,000	5,000	5,000	16,500	20,000	42,000
Noninterest income	17,613	15,589	15,770	17,880	15,012	14,718	13,746	15,539	66,852	59,015	62,753
Noninterest expense	32,269	30,394	29,779	27,202	27,991	25,724	25,185	25,665	119,644	104,565	105,210
Income before income taxes	7,473	7,240	6,765	11,376	8,499	11,721	11,402	13,221	32,854	44,843	32,694
Income taxes	2,556	2,331	1,877	3,733	2,753	4,151	3,955	4,111	10,497	14,970	9,464
Net income	4,917	4,909	4,888	7,643	5,746	7,570	7,447	9,110	22,357	29,873	23,230
Preferred stock dividends and discount accretion	908	909	908	908	1,234	1,049	1,283	1,776	3,633	5,342	5,170
Income available for common stockholders	$ 4,009	$ 4,000	$ 3,980	$ 6,735	$ 4,512	$ 6,521	$ 6,164	$ 7,334	$ 18,724	$ 24,531	$ 18,060
Basic earnings per share (in dollars per share)	$ 0.05	$ 0.05	$ 0.05	$ 0.08	$ 0.05	$ 0.08	$ 0.07	$ 0.09	$ 0.22	$ 0.29	$ 0.27
Diluted earnings per share (in dollars per share)	$ 0.05	$ 0.05	$ 0.05	$ 0.08	$ 0.05	$ 0.08	$ 0.07	$ 0.09	$ 0.22	$ 0.29	$ 0.27