Parent Corporation Only Financial Statements (Details) - Condensed Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 10,580	$ 13,077	$ 7,683	$ 11,880	$ (2,024)	$ 11,856	$ 10,859	$ 10,391	$ 43,220	$ 31,082	$ 41,311
Adjustments to reconcile net income to net cash provided by operating activities:
Increase in other assets									5,706	(15,006)	1,101
Increase (decrease) in other liabilities									3,887	(2,022)	(1,080)
Net cash provided by operating activities									131,133	49,712	46,231
Cash flows from investing activities:
Net cash used in investing activities									(817,727)	(427,669)	(504,747)
Cash flows from financing activities:
Cash dividends on common stock									(9,612)	(9,067)	(8,996)
Cash dividends on preferred stock										(22)	(112)
Issuance cost of common stock									180
Redemption of preferred stock										(11,250)
Proceeds from exercise of stock options									417	767	1,424
Net cash provided by financing activities									635,777	377,461	532,564
Decrease in cash and cash equivalents									(50,817)	(496)	74,048
Cash and cash equivalents at beginning of period									200,399	200,895	126,847
Cash and cash equivalents at end of period	149,582				200,399				149,582	200,399	200,895
Parent Company [Member]
Cash flows from operating activities:
Net income									43,220	31,082	41,311
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiary									(33,458)	(21,926)	(32,472)
Increase in other assets									269	2,023	(820)
Increase (decrease) in other liabilities									(151)	544	(1,840)
Net cash provided by operating activities									9,880	11,723	6,926
Cash flows from investing activities:
Purchase of available-for-sale securities									(7)
Capital infusion to subsidiary										(38,439)	(35,000)
Net cash used in investing activities									(7)	(38,439)	(35,000)
Cash flows from financing activities:
Proceeds from subordinated debt											50,000
Cash dividends on common stock									(9,612)	(9,067)	(8,996)
Cash dividends on preferred stock										(22)	(112)
Issuance cost of common stock									(180)
Secondary offering of common stock										38,439
Redemption of preferred stock										(11,250)
Proceeds from exercise of stock options									417	767	1,424
Net cash provided by financing activities									(9,375)	18,867	42,316
Decrease in cash and cash equivalents									498	(7,849)	14,583
Cash and cash equivalents at beginning of period									7,008	14,857	274
Cash and cash equivalents at end of period	$ 7,506				$ 7,008				$ 7,506	$ 7,008	$ 14,857