Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net income	$ 254,904	$ 238,167	$ 215,713
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	49,038	36,257	28,412
Provision for credit losses	74,973	43,240	38,148
Gain on sale of investments	(54,806)	(13,314)	(61)
Net accretion of investment securities and assets	(56,771)	(53,619)	(48,684)
Net amortization (accretion) on borrowings	541	394	(380)
Stock-based compensation expense	13,197	12,921	9,725
Gain on sale of premises and equipment, net of impairment	(14)	0	0
Gain on sale of foreclosed assets and other real estate owned	(391)	(33)	(650)
Gain on sale of mortgage loans held for sale	(44,864)	(20,064)	(12,844)
Gain on sale of other intangibles	(301)	0	0
Gain on sale of branches	(8,094)	0	0
Loss (gain) on sale of loans	0	4,451	(10)
Gain on sale of Visa, Inc. class B common stock	0	(42,860)
Fair value write-down of closed branches	434	0	836
Deferred income taxes	(122)	34,911	8,412
Income from bank owned life insurance	(7,206)	(4,854)	(5,003)
Originations of mortgage loans held for sale	(1,206,818)	(755,500)	(546,676)
Proceeds from sale of mortgage loans held for sale	1,172,406	756,642	556,759
Changes in assets and liabilities:
Interest receivable	(10,846)	3,231	(6,227)
Other assets	(7,480)	31,920	(35,113)
Accrued interest and other liabilities	50,508	(35,886)	33,978
Income taxes payable	(15,745)	20,074	(9,355)
Net cash provided by operating activities	202,543	256,078	226,980
INVESTING ACTIVITIES
Net collections (originations) of loans	1,327,248	23,806	(912,793)
Proceeds from sale of loans	49,736	104,587	24,977
Decrease (increase) in due from banks - time	2,975	1,130	(1,620)
Purchases of premises and equipment, net	(13,272)	(67,831)	(29,740)
Proceeds from sale of premises and equipment	369	0	0
Proceeds from sale of foreclosed assets and other real estate owned	10,788	17,986	27,751
Proceeds from sale of available-for-sale securities	1,717,364	1,226,578	0
Proceeds from maturities of available-for-sale securities	2,346,930	793,270	258,182
Purchases of available-for-sale securities	(4,140,963)	(1,708,948)	(784,113)
Proceeds from maturities of held-to-maturity securities	13,970	31,969	80,803
Purchases of held-to-maturity securities	(308,854)	0	(1,172)
Proceeds from bank owned life insurance death benefits	2,018	2,435	1,814
Purchases of bank owned life insurance	0	0	(4,000)
Cash received in business combinations	0	178,260	0
Disposition of assets and liabilities held for sale	181,560	1,235	(55,211)
Net cash provided by (used in) investing activities	1,189,869	604,477	(1,395,122)
FINANCING ACTIVITIES
Net change in deposits	1,086,713	(404,826)	1,305,877
Proceeds from issuance of subordinated notes and other borrowings	0	25,500	326,355
Repayments of subordinated debentures and subordinated debt	(7,442)	0	(113,990)
Dividends paid on preferred stock	(52)	(339)	0
Dividends paid on common stock	(74,593)	(63,921)	(55,646)
Net change in other borrowed funds	45,983	(240,806)	(34,574)
Net change in federal funds purchased and securities sold under agreements to repurchase	148,966	40,207	(26,652)
Net shares (cancelled) issued under stock compensation plans	(4,087)	(2,389)	1,162
Shares issued under employee stock purchase plan	956	1,312	1,026
Repurchase of common stock	(113,327)	(10,128)	0
Retirement of preferred stock	0	(42,000)	0
Net cash provided by (used in) financing activities	1,083,117	(697,390)	1,403,558
INCREASE IN CASH EQUIVALENTS	2,475,529	163,165	235,416
CASH AND CASH EQUIVALENTS, BEGINNING OF YEAR	996,623	833,458	598,042
CASH AND CASH EQUIVALENTS, END OF YEAR	$ 3,472,152	$ 996,623	$ 833,458