Derivative Activities - Offsetting of Derivative Assets - Derivative Assets, Financial Assets, and Collateral Held by Counterparty (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Total
Net amounts of assets presented in the balance sheet	$ 73,618	$ 78,179
Net amount	73,618	78,179
Deutsche Bank AG
Total
Net amounts of assets presented in the balance sheet	26,475	10,656
Net amount	26,475	10,656
RJ O'Brien
Total
Net amounts of assets presented in the balance sheet	3,125	4,508
Net amount	3,125	4,508
Citibank, N.A.
Total
Net amounts of assets presented in the balance sheet	1,222
Net amount	1,222
JP Morgan
Total
Net amounts of assets presented in the balance sheet		267
Net amount		267
Goldman Sachs
Total
Net amounts of assets presented in the balance sheet	646	540
Net amount	646	540
Morgan Stanley Bank
Total
Net amounts of assets presented in the balance sheet	587
Net amount	587
Federal National Mortgage Association
Total
Net amounts of assets presented in the balance sheet		1,092
Net amount		1,092
Other
Total
Net amounts of assets presented in the balance sheet	488	1,104
Net amount	488	1,104
Interest rate lock commitments
Total
Net amounts of assets presented in the balance sheet	41,075	60,012
Net amount	$ 41,075	$ 60,012