Derivative Activities - Offsetting of Derivative Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives not subject to master netting arrangements
Gross amounts of recognized assets	$ 67,550	$ 70,668
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	25,264	14,378
Gross amounts offset in the consolidated balance sheet	(19,196)	(6,867)
Net amounts of assets presented in the consolidated balance sheet	6,068	7,511
Total
Gross amounts of recognized assets	92,814	85,046
Net amounts of assets presented in the balance sheet	73,618	78,179
Interest rate lock commitments
Derivatives not subject to master netting arrangements
Gross amounts of recognized assets	41,075	60,012
Total
Net amounts of assets presented in the balance sheet	41,075	60,012
Repurchase agreement derivatives
Derivatives not subject to master netting arrangements
Gross amounts of recognized assets	26,475	10,656
MBS put options
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	4,413	3,481
Net amounts of assets presented in the consolidated balance sheet	4,413	3,481
Total
Gross amounts of recognized assets	4,413	3,481
MBS call options
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	12
Net amounts of assets presented in the consolidated balance sheet	12
Total
Gross amounts of recognized assets	12
Forward contracts | Purchases
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	821	4,288
Net amounts of assets presented in the consolidated balance sheet	821	4,288
Total
Gross amounts of recognized assets	821	4,288
Forward contracts | Sales
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	16,892	2,101
Net amounts of assets presented in the consolidated balance sheet	16,892	2,101
Total
Gross amounts of recognized assets	16,892	2,101
Put options on interest rate futures | Purchases
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	3,063	3,570
Net amounts of assets presented in the consolidated balance sheet	3,063	3,570
Total
Gross amounts of recognized assets	3,063	3,570
Call options on interest rate futures | Purchases
Derivatives subject to master netting arrangements:
Gross amounts of recognized assets	63	938
Net amounts of assets presented in the consolidated balance sheet	63	938
Total
Gross amounts of recognized assets	63	938
Margin Deposits
Total
Gross amounts of recognized assets	$ (4,372)	$ 2,620