Consolidated statements of cash flows - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Cash flows from operating activities:
Net income	$ 52,874,000	$ 745,000
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization of fixed assets	2,056,000	1,612,000
Amortization of core deposit and other intangibles	1,440,000	1,203,000
Capitalization of mortgage servicing rights	(11,594,000)	(7,796,000)
Net change in fair value of mortgage servicing rights	(12,601,000)	20,736,000
Stock-based compensation expense	2,666,000	1,883,000
Provision for credit losses	(11,632,000)	27,964,000
Provision for credit losses on unfunded commitments	(2,222,000)	1,601,000
Provision for mortgage loan repurchases	440,000	372,000
Amortization (accretion) of premiums and discounts on acquired loans, net	58,000	(1,578,000)
Accretion of discounts and amortization of premiums on securities, net	2,150,000	906,000
Gain from securities, net	(83,000)	(63,000)
Originations of loans held for sale	(1,757,932,000)	(1,097,672,000)
Proceeds from sale of loans held for sale	1,648,695,000	1,070,137,000
Gain on sale and change in fair value of loans held for sale	(52,811,000)	(33,595,000)
Net gain or write-downs of other real estate owned	(496,000)	(51,000)
Loss on other assets	11,000	328,000
Provision for deferred income taxes	9,639,000	(8,088,000)
Changes in:
Other assets and interest receivable	(225,000)	(118,909,000)
Accrued expenses and other liabilities	(42,615,000)	38,567,000
Net cash used in operating activities	(172,182,000)	(101,698,000)
Activity in available-for-sale securities:
Maturities, prepayments and calls	61,040,000	27,657,000
Purchases	(131,268,000)	(29,632,000)
Net change in loans	85,150,000	52,701,000
Purchases of FHLB stock	(525,000)	0
Purchases of premises and equipment	(2,050,000)	(3,014,000)
Proceeds from the sale of other real estate owned	2,495,000	1,442,000
Net cash paid in business combinations (See Note 2)	0	(4,227,000)
Net cash provided by investing activities	14,842,000	44,927,000
Cash flows from financing activities:
Net increase in demand deposits	855,673,000	272,566,000
Net decrease in time deposits	(56,824,000)	(40,107,000)
Net (decrease) increase in securities sold under agreements to repurchase	(2,965,000)	4,955,000
Payment of subordinated debt, net of premium accretion	(40,000,000)	0
Accretion of subordinated debt fair value premium and amortization of issuance costs, net	(158,000)	0
(Payments on) proceeds from other borrowings	(15,000,000)	15,000,000
Share based compensation withholding payments	(1,715,000)	(838,000)
Net proceeds from sale of common stock under employee stock purchase program	833,000	446,000
Dividends paid	(5,269,000)	(2,838,000)
Net cash provided by financing activities	734,575,000	249,184,000
Net change in cash and cash equivalents	577,235,000	192,413,000
Cash and cash equivalents at beginning of the period	1,317,898,000	232,681,000	$ 232,681,000
Cash and cash equivalents at end of the period	1,895,133,000	425,094,000	1,317,898,000
Supplemental cash flow information:
Interest paid	14,794,000	10,997,000
Taxes paid	15,117,000	105,000
Supplemental noncash disclosures:
Transfers from loans to other real estate owned	1,395,000	365,000
Transfers from premises and equipment to other real estate owned	0	841,000
Loans provided for sales of other real estate owned	330,000	0
Transfers from loans to loans held for sale	2,521,000	3,101,000
Transfers from loans held for sale to loans	14,413,000	1,445,000
Stock consideration paid in business combination	0	35,041,000
Trade date payable - securities	0	8,273,000	$ 0
Dividends declared not paid on restricted stock units	38,000	28,000
Decrease to retained earnings for adoption of new accounting standards	0	25,018,000
Right-of-use assets obtained in exchange for operating lease liabilities	$ 157,000	$ 480,000