Fair Value Measurements - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2017
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments for estimated costs to sell collateral dependent impaired loans	6.00%
Estimated costs to sell foreclosed assets	6.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Adjustments for estimated costs to sell collateral dependent impaired loans	8.00%
Estimated costs to sell foreclosed assets	8.00%
U.S. government and agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Transfers from Level 2 to Level 1, amount		$ 20.4