Quarterly Results of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Summary of the unaudited quarterly results of operations
Interest income	$ 77,788	$ 74,300	$ 56,769	$ 54,166	$ 55,596	$ 56,358	$ 58,277	$ 56,178	$ 263,023	$ 226,409	$ 180,604
Interest expense	5,437	5,688	5,155	5,385	5,629	5,931	6,139	6,228	21,665	23,927	23,471
Net interest income	72,351	68,612	51,614	48,781	49,967	50,427	52,138	49,950	241,358	202,482	157,133
Provision for loan losses	1,750	750	1,175	1,075	1,050	2,217	1,450	1,450	4,750	6,167	10,350
Noninterest income	31,442	32,079	22,879	21,870	19,941	22,531	19,443	18,594	108,270	80,509	71,891
Noninterest expense	70,734	75,979	51,082	47,319	45,900	48,098	49,337	47,602	245,114	190,937	172,928
Income before income taxes	31,309	23,962	22,236	22,257	22,958	22,643	20,794	19,492	99,764	85,887	45,746
Income taxes	10,149	7,742	6,842	7,017	7,361	7,108	5,941	5,895	31,750	26,305	12,259
Net income	$ 21,160	$ 16,220	$ 15,394	$ 15,240	$ 15,597	$ 15,535	$ 14,853	$ 13,597	$ 68,014	$ 59,582	$ 33,487
Basic earnings per share (usd per share)	$ 0.53	$ 0.40	$ 0.49	$ 0.48	$ 0.49	$ 0.49	$ 0.47	$ 0.43	$ 1.89	$ 1.89	$ 1.23
Diluted earnings per share (usd per share)	$ 0.52	$ 0.40	$ 0.48	$ 0.48	$ 0.49	$ 0.49	$ 0.47	$ 0.43	$ 1.88	$ 1.88	$ 1.22