Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans not covered under loss-share agreements	$ 7,784,000		$ 29,606,000
Specific reserve included in allowance for loan losses	120,185,000	$ 49,835,000	52,162,000	$ 49,026,000
Impairment losses on mortgage servicing rights	9,571,000	0	1,836,000
Changes in fair value, gain (loss)	(12,709,000)	$ 769,000
Impaired Loans, not covered
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Specific reserve included in allowance for loan losses	$ 1,040,000		$ 2,258,000