Quarterly Results of Operations (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
Summary of the unaudited quarterly results of operations
Interest income	$ 57,076	$ 44,638	$ 39,945	$ 38,945	$ 39,676	$ 39,154	$ 39,978	$ 40,505	$ 180,604	$ 159,313	$ 170,687
Interest expense	6,408	5,890	5,541	5,564	5,723	6,022	6,568	7,662	23,403	25,975	41,401
Net interest income	50,668	38,748	34,404	33,381	33,953	33,132	33,410	32,843	157,201	133,338	129,286
Provision for loan losses	2,000	2,300	3,000	3,050	4,000	4,625	4,700	4,800	10,350	18,125	22,350
Noninterest income	18,341	18,935	17,317	17,378	18,072	18,014	16,238	16,387	71,971	68,711	64,699
Noninterest expense	51,129	46,613	37,734	37,600	38,497	38,631	36,710	36,621	173,076	150,459	136,960
Income before income taxes	15,880	8,770	10,987	10,109	9,528	7,890	8,238	7,809	45,746	33,465	34,675
Income taxes	4,620	2,133	2,968	2,538	2,247	853	1,893	1,835	12,259	6,828	9,043
Net income	$ 11,260	$ 6,637	$ 8,019	$ 7,571	$ 7,281	$ 7,037	$ 6,345	$ 5,974	$ 33,487	$ 26,637	$ 25,632
Basic earnings per share (usd per share)	$ 0.36	$ 0.24	$ 0.32	$ 0.30	$ 0.29	$ 0.28	$ 0.25	$ 0.24	$ 1.23	$ 1.06	$ 1.02
Diluted earnings per share (usd per share)	$ 0.36	$ 0.24	$ 0.32	$ 0.30	$ 0.29	$ 0.28	$ 0.25	$ 0.24	$ 1.22	$ 1.06	$ 1.02