Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
OPERATING ACTIVITIES
Net income	$ 215,713	$ 92,940	$ 96,814
Items not requiring (providing) cash
Stock-based compensation expense	9,725	10,681	3,418
Deferred income taxes	8,412	23,251	9,832
Changes in
Other assets	(1,414)	12,456	(8,206)
Net cash provided by operating activities	260,679	114,563	91,134
INVESTING ACTIVITIES
Net originations of loans	(912,793)	(719,219)	(368,162)
Repayment of (advances to) subsidiaries	(55,211)	0	0
Proceeds from maturities of available-for-sale securities	258,325	487,717	257,388
Purchases of available-for-sale securities	(825,914)	(854,708)	(861,572)
Net cash used in investing activities	(1,428,821)	(338,471)	(250,949)
FINANCING ACTIVITIES
Proceeds from issuance of subordinated notes	326,355	0	0
Dividends paid on preferred stock	0	0	(24)
Dividends paid on common stock	(55,646)	(35,116)	(28,743)
Redemption of preferred stock	0	0	(30,852)
Net cash provided by financing activities	1,403,558	536,291	193,212
INCREASE IN CASH EQUIVALENTS	235,416	312,383	33,397
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR	598,042	285,659	252,262
CASH AND CASH EQUIVALENTS, END OF YEAR	833,458	598,042	285,659
Parent Company
OPERATING ACTIVITIES
Net income	215,713	92,940	96,814
Items not requiring (providing) cash
Stock-based compensation expense	9,725	10,681	3,418
Depreciation and amortization	880	1,183	700
Deferred income taxes	26	1,190	(2,526)
Equity in undistributed net income of bank subsidiaries	(91,057)	(39,645)	(25,072)
Changes in
Other assets	1,524	8,585	2,816
Other liabilities	17,340	(6,769)	(1,358)
Net cash provided by operating activities	154,151	68,165	74,792
INVESTING ACTIVITIES
Net originations of loans	219	90	(1,710)
Net proceeds from (purchases of) premises and equipment	3,342	(18)	(6,896)
Repayment of (advances to) subsidiaries	2,667	(15,000)	0
Proceeds from maturities of available-for-sale securities	152	42	1,973
Purchases of available-for-sale securities	(211)	(2,752)	(3)
Cash paid in business combinations	0	(100,468)	(35,048)
Other, net	(1,903)	0	0
Net cash used in investing activities	4,266	(118,106)	(41,684)
FINANCING ACTIVITIES
Proceeds from issuance of subordinated notes	326,355	0	0
Issuance (repayment) of long-term debt, net	(231,352)	8,014	(4,544)
Issuance of common stock, net	2,188	2,878	4,938
Dividends paid on preferred stock	0	0	(24)
Dividends paid on common stock	(55,646)	(35,116)	(28,743)
Redemption of preferred stock	0	0	(30,852)
Net cash provided by financing activities	41,545	(24,224)	(59,225)
INCREASE IN CASH EQUIVALENTS	199,962	(74,165)	(26,117)
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR	19,101	93,266	119,383
CASH AND CASH EQUIVALENTS, END OF YEAR	$ 219,063	$ 19,101	$ 93,266