Derivative Financial Instruments - Offsetting of Derivative Assets - Offsetting of Derivative and Financial Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Derivatives: Subject to master netting arrangements:
Gross amounts of recognized liabilities	$ 346,664	$ 37,085
Netting	(305,939)	(16,616)
Net amounts of liabilities presented in the balance sheet	40,725	20,469
Total
Gross amounts of recognized liabilities	349,091	38,946
Net amounts of liabilities presented in the consolidated balance sheet	43,152	22,330
Mortgage loans sold under agreements to repurchase
Net amounts of liabilities presented in the consolidated balance sheet	4,446,795	4,141,680
Debt Issuance Costs
Debt issuance costs, gross	(2,250)	(627)
Debt issuance costs	(2,250)	(627)
Debt issuance costs	(2,250)	(627)
Gross amounts of recognized liabilities	4,444,545	4,141,053
Net amount of liabilities in the consolidated balance sheet	4,444,545	4,141,053
Total
Gross amounts of recognized liabilities	4,793,636	4,179,999
Gross amounts offset in the consolidated balance sheet	(305,939)	(16,616)
Net amounts of liabilities presented in the consolidated balance sheet	4,489,947	4,164,010
Net amount of liabilities in the consolidated balance sheet	43,152	22,330
Receivable from Counterparties
Total
Net amounts of liabilities presented in the consolidated balance sheet	4,487,697	4,163,383
Assets sold under agreements to repurchase
Mortgage loans sold under agreements to repurchase
Gross amounts of recognized liabilities	4,446,795	4,141,680
Net amounts of liabilities presented in the consolidated balance sheet	4,446,795	4,141,680
Forward contracts | Purchases
Derivatives: Subject to master netting arrangements:
Gross amounts of recognized liabilities	12,553	19,040
Net amounts of liabilities presented in the balance sheet	12,553	19,040
Total
Gross amounts of recognized liabilities	12,553	19,040
Forward contracts | Sales
Derivatives: Subject to master netting arrangements:
Gross amounts of recognized liabilities	334,111	18,045
Net amounts of liabilities presented in the balance sheet	334,111	18,045
Total
Gross amounts of recognized liabilities	334,111	18,045
Interest rate lock commitments
Derivatives not subject to master netting arrangements
Gross amounts of recognized liabilities	2,427	1,861
Total
Net amounts of liabilities presented in the consolidated balance sheet	2,427	1,861
Net amount of liabilities in the consolidated balance sheet	$ 2,427	$ 1,861