Allowance for Credit Losses on Off-Balance Sheet Credit Exposures (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision for credit losses for off-balance sheet credit exposure					$ 0
Retained earnings	$ 685,509		$ 685,509			$ 695,273
Provision for credit losses	10,900	$ 9,500	25,617	$ 9,700
Cumulative Effect, Period of Adoption, Adjusted Balance
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision for credit losses for off-balance sheet credit exposure					3,206
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision for credit losses for off-balance sheet credit exposure					3,206
Retained earnings					8,300
Accounting Standards Update 2016-13
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Provision for credit losses for off-balance sheet credit exposure					3,200
Accounting Standards Update 2016-13, Effect On Off-Balance Sheet Items
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings					$ 2,400
Provision for credit losses	$ 5,300		$ 6,300