Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Statement of Cash Flows [Abstract]
Repayments of Other Debt	$ 0	$ 42,000
Cash flows from operating activities
Net income	132,536	140,584
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for loan losses	9,561	15,828
Gains on sales of loans	(11,538)	(5,531)
Proceeds from sales of loans	392,730	392,570
Valuation change in loans held-for-sale	1,730	216
Loans originated for sale, net of repayments	(330,969)	(379,584)
Net gains on sale of investment securities	(4,247)	(3)
Net (gains) losses from sales/writedowns of other real estate and repossessed assets	(807)	98
Depreciation of premises and equipment	8,527	8,384
Amortization of intangible assets	2,721	2,864
Additions to loan servicing rights	(4,242)	(4,251)
Valuation change in loan servicing rights	14,597	(2,272)
Net amortization of premiums and discounts on investment securities	12,744	9,123
Share-based compensation expense	5,129	4,078
Deferred income tax expense	3,783	4,473
Change in deferred tax valuation allowance	0	(72)
Net increase in interest receivable and other assets	(126,406)	(15,498)
Net increase (decrease) in interest payable and other liabilities	101,202	(5,671)
Net cash provided by operating activities	207,051	165,336
Investment securities - carried at fair value
Proceeds from maturities, calls and principal reductions	338,123	157,185
Proceeds from sales and redemptions	205,331	4,215
Purchases	(772,263)	(775,497)
Investment securities – held-to-maturity:
Proceeds from maturities, calls and principal reductions	1,880	85,027
Purchases	(1,549)	(11,240)
Net increase in loans	(602,373)	(439,390)
Proceeds from sales of other real estate and repossessed assets	5,311	7,646
Purchases of premises and equipment, net of disposals	(8,793)	(7,458)
Proceeds from returns of investment in equity method investments	162	269
Net cash used in investing activities	(834,171)	(979,243)
Cash flows from financing activities
Net increase in interest- and noninterest-bearing demand deposits and savings accounts	388	247,254
Net increase in time deposits	285,766	661,479
Net increase in collateralized customer deposits and other short-term borrowings	488,984	58,702
Cash dividends paid	(48,973)	(40,137)
Proceeds from directors’ stock plans and exercise of stock options, net of shares withheld	520	2,558
Cash paid for payroll taxes upon conversion of share-based awards	(2,646)	(4,660)
Net cash provided by financing activities	724,039	883,196
Net increase in cash and cash equivalents	96,919	69,289
Cash and cash equivalents at beginning of period	495,839	455,991
Cash and cash equivalents at end of period	592,758	525,280
Supplemental disclosures of cash flow information:
Interest paid	107,783	56,575
Net income tax (refunds) payments	(4,709)	4,599
Non-cash activities:
Loans transferred to other real estate and repossessed assets	6,729	5,093
Net transfer of loans held-for-sale to (from) loans held-for-investment	$ 58
Net transfer of loans held-for-sale to (from) loans held-for-investment		$ (2,171)