Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net income	$ 230,178	$ 213,780	$ 216,672
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan and lease losses	8,600	9,900	11,100
Depreciation, amortization, and accretion, net	52,176	25,675	25,917
Deferred income taxes	3,318	(15,587)	(10,586)
Stock compensation	4,507
Other gains, net	(51)	(2,514)
Originations of loans held for sale		(160,481)	(104,781)
Proceeds from sales of loans held for sale		167,215	103,106
Net gains on sales of loans held for sale		(3,650)	(2,003)
Net gains on investment securities	(27,277)	(12,321)	(20,822)
Change in assets and liabilities:
Net increase in other assets	(49,717)	(79,942)	(89)
Net (decrease) increase in other liabilities	(1,787)	528	28,237
Net cash provided by operating activities	219,947	142,603	246,751
Available-for-sale securities:
Proceeds from maturities and principal repayments	1,187,912	1,394,433	1,151,944
Proceeds from sales	832,891	2,471,753	61,936
Purchases	(3,108,687)	(2,916,767)	(2,233,733)
Other investments:
Proceeds from sales	23,203	40,712	21,226
Purchases	(26,334)	(33,880)	(12,808)
Net increase in loans and leases resulting from originations and principal repayments	(801,973)	(704,224)	(506,777)
Proceeds from sales of loans originated for investment	291		3,768
Proceeds from bank owned life insurance	10,357		1,922
Purchases of premises, equipment, and software	(15,541)	(19,119)	(20,740)
Proceeds from sales of premises and equipment	71	3,214
Purchases of mortgage servicing rights			(14,579)
Proceeds from sales of other real estate owned	1,031	7,620	3,347
Other	94	90	2,345
Net cash (used in) provided by investing activities	(1,896,685)	243,832	(1,542,149)
Cash flows from financing activities
Net increase in deposits	732,608	1,336,545	1,147,033
Net decrease in short-term borrowings	(207,000)	(170,000)	(207,056)
Repayment of long-term debt	(10)	(10)	(6)
Dividends paid	(85,797)
Distributions paid	(361,200)	(164,228)	(192,527)
Net cash provided by financing activities	78,601	1,002,307	747,444
Net (decrease) increase in cash and cash equivalents	(1,598,137)	1,388,742	(547,954)
Cash and cash equivalents at beginning of year	2,650,195	1,261,453	1,809,407
Cash and cash equivalents at end of year	1,052,058	2,650,195	1,261,453
Supplemental disclosures
Interest paid	25,870	22,086	24,081
Income taxes paid, net of income tax refunds	190,387	187,100	93,959
Noncash investing and financing activities:
Transfers from loans and leases to other real estate owned	1,056	2,470	5,534
Transfers of loans and leases (from) to loans held for sale, net	(291)	$ (3,260)	$ 2,916
Derivative liability entered into in connection with sale of investment securities	$ 8,828