Transfers Accounted for as Secured Borrowings (Details) - U.S. Government-sponsored mortgage-backed securities - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	$ 183,589	$ 177,102
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	183,589	175,449
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	0	1,653
Greater Than 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Collateral pledged for all repurchase agreements accounted for as secured borrowings	$ 0	$ 0