Consolidated Statements of Cash Flow - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net income	$ 264,394	$ 183,682	$ 230,178
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	22,180	18,500	8,600
Depreciation, amortization and accretion, net	54,903	62,019	52,176
Deferred income taxes	(3,602)	58,916	3,318
Stock-based compensation	6,185	5,292	4,507
Net gains on sale of real estate		(6,922)
Other gains	(1,062)	(210)	(51)
Originations of loans held for sale	(29,707)
Proceeds from sales of loans held for sale	29,467
Net gains on sales of loans held for sale	(199)	(16)
Net gains on investment securities			(27,277)
OTTI losses on available-for-sale debt securities	24,085
Change in assets and liabilities:
Net decrease (increase) in other assets	11,859	(42,359)	(49,571)
Net decrease in other liabilities	(27,090)	(9,128)	(1,787)
Net cash provided by operating activities	351,413	269,774	220,093
Available-for-sale securities:
Proceeds from maturities and principal repayments	810,260	888,700	1,187,912
Proceeds from sales			832,891
Purchases	(130,252)	(1,088,417)	(3,108,687)
Other investments:
Proceeds from sales	12,842	15,517	23,203
Purchases	(65,239)	(20,487)	(26,334)
Loans:
Net increase in loans and leases resulting from originations and principal repayments	(572,488)	(750,917)	(801,973)
Proceeds from sales of loans originated for investment	562	9,711	291
Purchases of loans	(270,272)	(26,626)
Proceeds from bank-owned life insurance	1,151	4,482	10,357
Purchases of premises, equipment and software	(35,880)	(10,068)	(15,541)
Proceeds from sales of premises and equipment	65	8,139	71
Purchases of mortgage servicing rights	(6,444)
Proceeds from sales of other real estate owned	718	929	1,031
Other	(2,832)	(2,044)	94
Net cash used in investing activities	(257,809)	(971,081)	(1,896,685)
Cash flows from financing activities
Net (decrease) increase in deposits	(462,054)	817,590	732,608
Net decrease in short-term borrowings		(9,151)	(207,000)
Proceeds from long-term borrowings	600,000
Repayment of long-term borrowings	(10)	(10)	(10)
Dividends paid	(131,036)	(122,810)	(85,797)
Distributions paid		(2,118)	(361,200)
Stock tendered for payment of withholding taxes	(53)	(136)	(146)
Proceeds from employee stock purchase plan	342	528
Common stock repurchased	(131,800)
Net cash (used in) provided by financing activities	(124,611)	683,893	78,455
Net (decrease) increase in cash and cash equivalents	(31,007)	(17,414)	(1,598,137)
Cash and cash equivalents at beginning of period	1,034,644	1,052,058	2,650,195
Cash and cash equivalents at end of period	1,003,637	1,034,644	1,052,058
Supplemental disclosures
Interest paid	80,381	36,633	25,870
Income taxes paid, net of income tax refunds	43,002	145,072	190,387
Noncash investing and financing activities:
Transfers from loans and leases to other real estate owned	$ 549	759	1,056
Transfers from loans and leases to loans held for sale		$ 10,251	291
Derivative liability entered into in connection with sale of investment securities			$ 8,828