Transfers Accounted for as Secured Borrowings (Details) - U.S. Government-sponsored mortgage-backed securities - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	$ 187,732	$ 187,946
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	186,081	178,732
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	0	0
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	1,651	7,672
Greater Than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	$ 0	$ 1,542