Fair Value Measurements, Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Mortgage servicing rights	$ 49,541		$ 41,990
Mortgage banking, net	(10,578)	$ 9,098
Equity securities	14,000		13,000
Investment securities gains (losses), net	15,673		15,106
Fair Value, Inputs, Level 3
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Equity securities	13,989		13,444
Investment securities gains (losses), net	13,989		13,444
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 2
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
OREO(b)	10,326		6,125
Other noninterest expense	3,681		3,747
Fair Value, Nonrecurring [Member] | Fair Value, Inputs, Level 3
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Individually evaluated loans(a)	93,201		138,752
Provision for credit losses	(1,613)		97,519
Mortgage servicing rights	49,541		41,990
Mortgage banking, net	$ 10,578		$ (17,704)