CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net income	$ 185,754	$ 284,392	$ 264,394
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for credit losses	121,718	13,800	22,180
Depreciation, amortization and accretion, net	63,071	67,824	54,903
Deferred income tax (benefit) provision	(19,396)	17,060	(3,602)
Stock-based compensation	10,028	7,826	6,185
Other (gains) losses	(4)	19	(1,062)
Originations of loans held for sale	(327,076)	(19,164)	(29,707)
Proceeds from sales of loans held for sale	326,785	18,156	29,467
Net (gains) losses on sales of loans originated for investment and held for sale	(18,995)	1,102	(199)
Net losses on investment securities	114	2,715
OTTI losses on available-for-sale debt securities			24,085
Change in assets and liabilities:
Net (increase) decrease in other assets	(17,880)	(20,923)	11,859
Net decrease in other liabilities	(114,613)	(76,303)	(27,090)
Net cash provided by operating activities	209,506	296,504	351,413
Available-for-sale securities:
Proceeds from maturities and principal repayments	1,474,587	767,892	810,260
Proceeds from calls and sales	644,983	1,070,715
Purchases	(4,045,871)	(1,301,041)	(130,252)
Other investments:
Proceeds from sales	34,822	14,292	12,842
Purchases	(77,927)	(30,996)	(65,239)
Loans:
Net increase in loans and leases resulting from originations and principal repayments	(217,530)	(133,702)	(572,488)
Proceeds from sales of loans originated for investment	153,647	407,698	562
Purchases of loans	(41,146)	(398,735)	(270,272)
Proceeds from bank-owned life insurance	3,089	7,682	1,151
Purchases of premises, equipment and software	(33,390)	(29,354)	(35,880)
Purchases of mortgage servicing rights			(6,444)
Proceeds from sales of other real estate owned	787	759	718
Other	186	2	(2,767)
Net cash (used in) provided by investing activities	(2,103,763)	375,212	(257,809)
Cash flows from financing activities
Net increase (decrease) in deposits	2,782,729	(705,074)	(462,054)
Repayment of short-term borrowings	(400,000)
Proceeds from long-term borrowings			600,000
Repayment of long-term borrowings	(9)	(10)	(10)
Dividends paid	(135,099)	(138,246)	(131,036)
Stock tendered for payment of withholding taxes	(1,749)	(1,764)	(53)
Proceeds from employee stock purchase plan	312		342
Common stock repurchased	(5,000)	(136,242)	(131,800)
Net cash provided by (used in) financing activities	2,241,184	(981,336)	(124,611)
Net increase (decrease) in cash and cash equivalents	346,927	(309,620)	(31,007)
Cash and cash equivalents at beginning of year	694,017	1,003,637	1,034,644
Cash and cash equivalents at end of year	1,040,944	694,017	1,003,637
Supplemental disclosures
Interest paid	52,865	102,457	80,381
Income taxes paid, net of income tax refunds	53,272	70,508	43,002
Noncash investing and financing activities:
Transfers from loans and leases to other real estate owned	437	310	549
Operating lease right-of-use assets obtained in exchange for new lease obligations	3,796	1,401
Transfers from loans and leases to loans held for sale	145,036	408,264
Obligation to fund low-income housing partnerships	$ 13,767	$ 31,628	$ 36,044