Fair Value Measurements - Narrative (Details) - USD ($)	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Mar. 31, 2020	Mar. 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	$ 9,563,000		$ 29,606,000
Specific reserve included in allowance for loan losses	145,387,000	$ 50,059,000	52,162,000	$ 120,185,000	$ 49,835,000	$ 49,026,000
Impairment losses on mortgage servicing rights	14,522,000	0	1,836,000
Changes in fair value, gain	9,617,000	$ 3,543,000
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	$ 2,084,000		$ 2,258,000