Consolidated Statements of Cash Flows - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING ACTIVITIES
Net income		$ 286,502	$ 243,600	$ 195,513
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	[1]	130,500	32,850	70,750
Net amortization (accretion) of premiums and discounts from acquisition		251	215	(398)
Depreciation and amortization		62,803	56,258	53,116
Amortization of debt issuance costs		131
Deferred income tax benefit		(4,836)	(153)	(20,261)
Net decrease (increase) in trading securities and other earning assets		10,598	15,393	(6,956)
Gains on investment securities, net		(120,634)	(2,245)	(3,521)
Gains on sales of assets		(797)	(374)	(2,721)
Amortization of securities premiums, net of discount accretion		44,302	33,441	42,423
Originations of loans held for sale		(128,123)	(216,334)	(59,687)
Gains on sales of loans held for sale, net		(3,964)	(1,370)	(1,183)
Proceeds from sales of loans held for sale		133,182	213,093	59,138
Equity based compensation		15,120	14,850	11,074
Net tax benefit related to equity compensation plans		345	766	2,364
Changes in:
Accrued income		(15,384)	(14,340)	(11,305)
Accrued expenses and taxes		91,693	76,846	(13,747)
Other assets and liabilities, net		(128,091)	(112,563)	(18,903)
Net cash provided by operating activities		373,598	339,933	295,696
Securities held to maturity:
Maturities, calls and principal repayments		193,629	208,009	114,427
Purchases		(92,141)	(156,143)	(24,059)
Securities available for sale:
Sales		315,890	411,981	95,525
Maturities, calls and principal repayments		2,455,185	1,251,051	1,016,139
Purchases		(4,373,394)	(2,346,927)	(1,486,486)
Equity securities with readily determinable fair values:
Maturities, calls and principal repayments		50,047	3,487	53
Purchases		(75,177)
Equity securities without readily determinable fair values:
Maturities, calls and principal repayments		16,735	1,979	2,561
Purchases		(9,145)	(24,075)	(5,190)
Payment on low-income housing tax credit (LIHTC) investment commitments		(42,995)	(4,826)	(1,653)
Net increase in loans		(2,693,761)	(1,284,818)	(970,399)
Net increase in fed funds sold and resell agreements		(71,990)	(951,344)	(435,400)
Net cash activity from acquisitions and divestiture		24	(18,498)	(8,907)
Net (increase) decrease in interest-bearing balances due from other financial institutions		(13,835)	(10,447)	9,389
Purchases of bank premises and equipment		(60,216)	(72,313)	(57,940)
Proceeds from sales of bank premises and equipment		8,568	5,536	5,379
Purchases of bank-owned and company-owned life insurance		(100,000)
Proceeds from bank-owned and company-owned life insurance death benefit		1,489	2,187	16
Net cash used in investing activities		(4,491,087)	(2,985,161)	(1,746,545)
FINANCING ACTIVITIES
Net increase in demand and savings deposits		5,798,276	2,242,368	1,402,119
Net (decrease) increase in time deposits		(350,269)	79,616	(129,159)
Net increase in fed funds purchased and repurchase agreements		418,989	377,588	258,216
Proceeds from short-term debt		15,000
Repayment of short-term debt		(15,000)
Proceeds from long-term debt		200,000
Payment of debt issuance costs		(2,250)
Cash dividends paid		(60,281)	(59,436)	(58,279)
Proceeds from exercise of stock options and sales of treasury shares		5,186	4,637	12,318
Purchases of treasury stock		(63,766)	(4,496)	(76,507)
Net cash provided by financing activities		5,945,885	2,640,277	1,408,708
Increase (decrease) in cash and cash equivalents		1,828,396	(4,951)	(42,141)
Cash and cash equivalents at beginning of year		1,669,170	1,674,121	1,716,262
Cash and cash equivalents at end of year		3,497,566	1,669,170	1,674,121
Supplemental disclosures:
Income tax payments		34,068	2,245	63,127
Total interest payments		84,105	189,582	115,163
Noncash disclosures:
Acquisition of low-income housing tax credit investments		59,072	18,602	4,000
Commitment to fund low-income housing tax credit investments		$ 59,072	$ 18,602	$ 4,000

[1] For the years ended December 31, 2019 and 2018, this line represents the Provision for loan losses. See further discussion of this change in Note 2, “New Accounting Pronouncements.”