Condensed Financial Statements of Parent Company - Condensed Statements of Cash Flows - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 87,554	$ 101,282	$ 99,473
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	28,704	21,582	21,470
Share-based Compensation.	6,934	6,220	5,803
Gain on sale of securities available for sale	(1,421)	(122)
Decrease (increase) in other assets	(32,324)	(13,799)	(4,861)
Decrease in Other Liabilities	7,076	9,068	(1,951)
Net cash provided by operating activities	197,890	138,011	186,868
Cash flows from investing activities:
Proceeds from calls of other investment securities			1,392
Net cash received from acquisitions	185,163		403,548
Net cash provided by (used in) investing activities	(60,900)	(690,919)	(103,015)
Cash flows from financing activities:
Repayment of other borrowings	(390,811)	(14)	(46,398)
Common stock issuance	1,055	925	908
Common stock repurchase	(5,512)	(5,981)	(5,631)
Dividends paid on common stock	(38,623)	(29,285)	(23,710)
Stock options exercised	1,965	2,204	1,115
Net cash provided by financing activities	(133,811)	231,562	194,072
Net increase (decrease) in cash and cash equivalents	3,179	(321,346)	277,925
Cash and cash equivalents at beginning of period	374,448	695,794	417,869
Cash and cash equivalents at end of period	377,627	374,448	695,794
Parent company
Cash flows from operating activities:
Net income	87,554	101,282	99,473
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	666	222	355
Share-based Compensation.	6,934	6,220	5,803
Gain on sale of securities available for sale	(486)	(122)
Decrease (increase) in other assets	(1,564)	26	(296)
Decrease in Other Liabilities	(6,341)	3,750	(1,648)
Undistributed earnings of subsidiary	(33,700)	(73,195)	(22,578)
Net cash provided by operating activities	53,063	38,183	81,109
Cash flows from investing activities:
Proceeds from calls of other investment securities	687	137	1,392
Payments for investments in subsidiary			(384)
Net cash received from acquisitions	15,468
Net cash provided by (used in) investing activities	16,155	137	1,008
Cash flows from financing activities:
Repayment of other borrowings	(30,000)		(46,392)
Common stock issuance	1,056	925	908
Common stock repurchase	(5,512)	(5,981)	(5,631)
Dividends paid on common stock	(38,623)	(29,285)	(23,710)
Stock options exercised	1,965	2,204	1,115
Net cash provided by financing activities	(71,114)	(32,137)	(73,710)
Net increase (decrease) in cash and cash equivalents	(1,896)	6,183	8,407
Cash and cash equivalents at beginning of period	27,775	21,592	13,185
Cash and cash equivalents at end of period	$ 25,879	$ 27,775	$ 21,592