Condensed Financial Information (Parent Company Only) - Condensed Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
OPERATING ACTIVITIES
Net income	$ 238,167	$ 215,713	$ 92,940
Items not requiring (providing) cash
Stock-based compensation expense	12,921	9,725	10,681
Deferred income taxes	34,911	8,412	23,251
Changes in:
Other assets	42,189	(1,414)	12,456
Net cash provided by operating activities	266,347	260,679	114,563
INVESTING ACTIVITIES
Net collections (originations) of loans	23,806	(912,793)	(719,219)
Repayment of (advances to) subsidiaries	1,235	(55,211)	0
Proceeds from maturities of available-for-sale securities	776,084	258,325	487,717
Purchases of available-for-sale securities	(1,710,483)	(825,914)	(854,708)
Net cash provided by (used in) investing activities	594,208	(1,428,821)	(338,471)
FINANCING ACTIVITIES
Proceeds from issuance of subordinated notes and other borrowings	25,500	326,355	0
Stock repurchases	10,128	0	0
Dividends paid on preferred stock	(339)	0	0
Dividends paid on common stock	(63,921)	(55,646)	(35,116)
Retirement of preferred stock	(42,000)	0	0
Net cash (used in) provided by financing activities	(697,390)	1,403,558	536,291
Parent Company
OPERATING ACTIVITIES
Net income	238,167	215,713	92,940
Items not requiring (providing) cash
Stock-based compensation expense	12,921	9,725	10,681
Depreciation and amortization	1,637	880	1,183
Deferred income taxes	(3,632)	26	1,190
Equity in undistributed net income of bank subsidiaries	(191,530)	(91,057)	(39,645)
Changes in:
Other assets	3,299	1,524	8,585
Other liabilities	(2,648)	17,340	(6,769)
Net cash provided by operating activities	58,214	154,151	68,165
INVESTING ACTIVITIES
Net collections (originations) of loans	117	219	90
Net (purchases of) proceeds from premises and equipment	(23,184)	3,342	(18)
Repayment of (advances to) subsidiaries	0	2,667	(15,000)
Proceeds from maturities of available-for-sale securities	2,544	152	42
Purchases of available-for-sale securities	(439)	(211)	(2,752)
Cash paid in business combinations	(36,811)	0	(100,468)
Other, net	29	(1,903)	0
Net cash provided by (used in) investing activities	(57,744)	4,266	(118,106)
FINANCING ACTIVITIES
Proceeds from issuance of subordinated notes and other borrowings	0	326,355	0
Issuance (repayment) of long-term debt, net	2,000	(231,352)	8,014
(Cancellation) issuance of common stock, net	(1,077)	2,188	2,878
Stock repurchases	10,128	0	0
Dividends paid on preferred stock	(339)	0	0
Dividends paid on common stock	(63,921)	(55,646)	(35,116)
Retirement of preferred stock	(42,000)	0	0
Net cash (used in) provided by financing activities	(115,465)	41,545	(24,224)
(DECREASE) INCREASE IN CASH AND CASH EQUIVALENTS	(114,995)	199,962	(74,165)
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR	219,063	19,101	93,266
CASH AND CASH EQUIVALENTS, END OF YEAR	$ 104,068	$ 219,063	$ 19,101