Consolidated Statements of Cash Flow - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 183,682	$ 230,178	$ 213,780
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	18,500	8,600	9,900
Depreciation, amortization and accretion, net	62,019	52,176	25,675
Deferred income taxes	58,916	3,318	(15,587)
Stock-based compensation	5,292	4,507
Net gains on sale of real estate	(6,922)
Other (gains) losses	(210)	(51)	(2,514)
Originations of loans held for sale			(160,481)
Proceeds from sales of loans held for sale			167,215
Net gains on sales of loans held for sale	(16)		(3,650)
Net gains on investment securities		(27,277)	(12,321)
Change in assets and liabilities:
Net increase in other assets (1)	(42,359)	(49,571)	(79,942)
Net increase (decrease) in other liabilities	(9,128)	(1,787)	528
Net cash provided by operating activities	269,774	220,093	142,603
Available-for-sale securities:
Proceeds from maturities and principal repayments	888,700	1,187,912	1,394,433
Proceeds from sales		832,891	2,471,753
Purchases	(1,088,417)	(3,108,687)	(2,916,767)
Other investments:
Proceeds from sales	15,517	23,203	40,712
Purchases	(20,487)	(26,334)	(33,880)
Loans:
Net increase in loans and leases resulting from originations and principal repayments	(750,917)	(801,973)	(704,224)
Proceeds from sales of loans originated for investment	9,711	291
Purchases of loans	(26,626)
Proceeds from bank-owned life insurance	4,482	10,357
Purchases of premises, equipment and software	(10,068)	(15,541)	(19,119)
Proceeds from sales of premises and equipment	8,139	71	3,214
Proceeds from sales of other real estate owned	929	1,031	7,620
Other	(2,044)	94	90
Net cash provided by (used in) investing activities	(971,081)	(1,896,685)	243,832
Cash flows from financing activities
Net increase in deposits	817,590	732,608	1,336,545
Net decrease in short-term borrowings	(9,151)	(207,000)	(170,000)
Repayment of long-term debt	(10)	(10)	(10)
Dividends paid	(122,810)	(85,797)
Distributions paid	(2,118)	(361,200)	(164,228)
Stock tendered for payment of withholding taxes (1)	(136)	(146)
Proceeds from employee stock purchase plan	528
Net cash provided by financing activities	683,893	78,455	1,002,307
Net increase (decrease) in cash and cash equivalents	(17,414)	(1,598,137)	1,388,742
Cash and cash equivalents at beginning of year	1,052,058	2,650,195	1,261,453
Cash and cash equivalents at end of year	1,034,644	1,052,058	2,650,195
Supplemental disclosures
Interest paid	36,633	25,870	22,086
Income taxes paid, net of income tax refunds	145,072	190,387	187,100
Noncash investing and financing activities:
Transfers from loans and leases to other real estate owned	759	1,056	2,470
Transfers of loans and leases to loans held for sale	$ 10,251	(291)	$ (3,260)
Derivative liability entered into in connection with sale of investment securities		$ 8,828