Unaudited Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Summarized unaudited quarterly financial data
Interest income	$ 73,939	$ 69,531	$ 62,151	$ 57,955	$ 59,666	$ 62,015	$ 64,192	$ 67,884	$ 263,576	$ 253,757	$ 280,109
Interest expense	6,929	7,186	7,185	7,458	8,165	8,907	9,044	9,598	28,758	35,714	44,494
Net Interest Income	67,010	62,345	54,966	50,497	51,501	53,108	55,148	58,286	234,818	218,043	235,615
Provision for loan losses	1,802	1,907	1,078	2,100	2,275	2,700	7,925	8,625	6,887	21,525	64,500
Net interest income after provision for loan losses	65,208	60,438	53,888	48,397	49,226	50,408	47,223	49,661	227,931	196,518	171,115
Noninterest Income	23,002	23,873	23,222	22,950	25,393	23,974	21,791	20,338	93,047	91,496	78,199
Noninterest Expense	53,034	50,368	48,481	43,434	48,008	50,178	46,190	49,045	195,317	193,421	232,124
Income Before Income Taxes	35,176	33,943	28,629	27,913	26,611	24,204	22,824	20,954	125,661	94,593	17,190
Federal and state income tax expense	8,630	8,315	5,927	7,145	5,853	4,760	3,843	4,621	30,017	19,077	(281)
Net Income	$ 26,546	$ 25,628	$ 22,702	$ 20,768	$ 20,758	$ 19,444	$ 18,981	$ 16,333	$ 95,644	$ 75,516	$ 17,471
Basic earnings per share	$ 0.36	$ 0.35	$ 0.31	$ 0.29	$ 0.29	$ 0.27	$ 0.26	$ 0.23	$ 1.31	$ 1.05	$ 0.24
Diluted earnings per share	$ 0.36	$ 0.35	$ 0.31	$ 0.29	$ 0.29	$ 0.27	$ 0.26	$ 0.23	$ 1.31	$ 1.05	$ 0.24