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, 2020	Mar. 31, 2019	Dec. 31, 2019
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Mortgage servicing rights	$ 58,311		$ 72,532
Mortgage banking, net	9,098	$ 121
Equity securities	13,000		13,000
Investment securities gains (losses), net	15,063		15,090
Fair Value, Inputs, Level 3
Assets and Liabilities Measured at Fair Value on a Non-recurring Basis
Equity securities	13,444		13,444
Investment securities gains (losses), net	13,444		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)	1,382		3,565
Other noninterest expense	(806)		(1,860)
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)	103,108		45,792
Provision for credit losses	(23,840)		(66,172)
Mortgage servicing rights	58,311		72,532
Mortgage banking, net	(9,098)		(63)
Equity securities	13,444		13,444
Investment securities gains (losses), net	$ 0		$ 13,444