Consolidated Statements of Cash Flows (Unaudited) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Operating activities
Net income	$ 57,908,000	$ 2,008,000
Adjustments to reconcile net income to net cash used in operating activities:
Provision for loan losses	0	26,350,000
Depreciation, amortization and accretion	10,059,000	4,937,000
Deferred income tax expense (benefit)	5,542,000	(2,791,000)
Funding of mortgage loans held for sale	(1,143,349,000)	(715,760,000)
Proceeds from sales of mortgage loans held for sale	1,082,538,000	607,017,000
Gains on sales of mortgage loans held for sale	(33,901,000)	(21,782,000)
Valuation adjustment to mortgage servicing rights	(13,561,000)	9,571,000	$ 11,726,000
Gains on sales of securities	(1,357,000)	0
Gains on sales of premises and equipment	(22,000)	0
Stock-based compensation expense	2,756,000	2,750,000
Increase in other assets	(11,800,000)	(70,631,000)
(Decrease) increase in other liabilities	(11,601,000)	35,331,000
Net cash used in operating activities	(56,788,000)	(123,000,000)
Investing activities
Purchases of securities available for sale	(465,245,000)	(123,670,000)
Proceeds from sales of securities available for sale	155,391,000	0
Proceeds from call/maturities of securities available for sale	95,382,000	76,269,000
Net decrease (increase) in loans	243,250,000	(69,337,000)
Purchases of premises and equipment	(2,630,000)	(1,941,000)
Proceeds from sales of premises and equipment	34,000	0
Net change in FHLB stock	(24,000)	(12,432,000)
Proceeds from sales of other assets	1,962,000	770,000
Other, net	1,346,000	0
Net cash provided by (used in) investing activities	29,466,000	(130,341,000)
Financing activities
Net increase in noninterest-bearing deposits	450,312,000	90,289,000
Net increase in interest-bearing deposits	227,515,000	109,115,000
Net (decrease) increase in short-term borrowings	(9,186,000)	313,946,000
Repayment of long-term debt	(42,000)	(43,000)
Cash paid for dividends	(12,564,000)	(12,555,000)
Repurchase of shares in connection with stock repurchase program	0	(24,569,000)
Net cash provided by financing activities	656,035,000	476,183,000
Net increase in cash and cash equivalents	628,713,000	222,842,000
Cash and cash equivalents at beginning of period	633,203,000	414,930,000	414,930,000
Cash and cash equivalents at end of period	1,261,916,000	637,772,000	$ 633,203,000
Supplemental disclosures
Cash paid for interest	15,108,000	26,264,000
Cash paid for income taxes	18,032,000	4,176,000
Noncash transactions:
Transfers of loans to other real estate owned	2,039,000	1,641,000
Financed sales of other real estate owned	0	159,000
Recognition of operating right-of-use assets	3,601,000	1,968,000
Recognition of operating lease liabilities	$ 3,601,000	$ 2,034,000