Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Operating activities
Net income	$ 20,130,000	$ 2,008,000	$ 46,625,000	$ 45,110,000	$ 22,138,000	$ 91,735,000
Adjustments to reconcile net income to net cash (used in) provided by operating activities:
Provision for credit losses on loans	26,900,000		900,000		53,250,000	2,400,000
Depreciation, amortization and accretion					13,247,000	1,607,000
Deferred income tax (benefit) expense					(9,812,000)	8,585,000
Funding of mortgage loans held for sale					(2,023,834,000)	(938,825,000)
Proceeds from sales of mortgage loans held for sale					2,024,141,000	856,243,000
Gains on sales of mortgage loans held for sale					(21,782,000)	(20,789,000)
Valuation adjustment to mortgage servicing rights					14,522,000	0	$ 1,836,000
Gains on sales of securities	(31,000)		8,000		(31,000)	(5,000)
Penalty on prepayment of debt	90,000		0		90,000	0
Loss (gains) on sales of premises and equipment					35,000	(1,073,000)
Stock-based compensation expense					5,748,000	4,719,000
Net change in other loans held for sale					0	55,792,000
Increase in other assets					(68,031,000)	(4,815,000)
Increase (decrease) in other liabilities					45,232,000	(10,762,000)
Net cash provided by operating activities					54,913,000	44,812,000
Investing activities
Purchases of securities available for sale					(182,745,000)	(125,503,000)
Proceeds from sales of securities available for sale	8,773,000		2,001,000		8,773,000	12,612,000
Proceeds from call/maturities of securities available for sale					183,807,000	120,738,000
Net (increase) decrease in loans					(1,296,880,000)	37,634,000
Purchases of premises and equipment					(3,856,000)	(16,491,000)
Proceeds from sales of premises and equipment					0	2,240,000
Net change in FHLB stock					(496,000)	8,710,000
Proceeds from sales of other assets					2,228,000	15,295,000
Other, net					0	2,000
Net cash (used in) provided by investing activities					(1,289,169,000)	55,237,000
Financing activities
Net increase in noninterest-bearing deposits					1,188,526,000	90,278,000
Net increase (decrease) in interest-bearing deposits					444,810,000	(28,100,000)
Net decrease in short-term borrowings					(147,281,000)	(248,695,000)
Repayment of long-term debt					(177,000)	(430,000)
Cash paid for dividends					(25,080,000)	(25,413,000)
Repurchase of shares in connection with stock repurchase program					(24,569,000)	(12,938,000)
Net cash provided by (used in) financing activities					1,436,229,000	(225,298,000)
Net increase (decrease) in cash and cash equivalents					201,973,000	(125,249,000)
Cash and cash equivalents at beginning of period		$ 414,930,000		$ 569,111,000	414,930,000	569,111,000	569,111,000
Cash and cash equivalents at end of period	$ 616,903,000		$ 443,862,000		616,903,000	443,862,000	$ 414,930,000
Supplemental disclosures
Cash paid for interest					43,564,000	47,599,000
Cash paid for income taxes					16,163,000	13,820,000
Noncash transactions:
Transfers of loans to other real estate owned					4,259,000	1,796,000
Financed sales of other real estate owned					154,000	254,000
Transfers of other loans held for sale to loans held for investment					0	189,000
Recognition of operating right-of-use assets					4,235,000	75,042,000
Recognition of operating lease liabilities					$ 2,766,000	$ 78,561,000