Resale and Repurchase Agreements Remaining Contractual Maturities of Repurchase Agreements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
U.S. Government and Federal Agency Obligations [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 146,935	$ 526,283
U.S. Government and Federal Agency Obligations [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
U.S. Government and Federal Agency Obligations [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
U.S. Government and Federal Agency Obligations [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	146,935	526,283
Government-Sponsored Enterprise Obligations [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	21,386	32,575
Government-Sponsored Enterprise Obligations [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Government-Sponsored Enterprise Obligations [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Government-Sponsored Enterprise Obligations [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	21,386	32,575
Agency Mortgage-Backed Securities [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	1,167,467	973,774
Agency Mortgage-Backed Securities [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	58,729	48,517
Agency Mortgage-Backed Securities [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	214,896	227,802
Agency Mortgage-Backed Securities [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	1,441,092	1,250,093
Non Agency Mortgage Backed Securities [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	98,651	71,399
Non Agency Mortgage Backed Securities [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Non Agency Mortgage Backed Securities [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Non Agency Mortgage Backed Securities [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	98,651	71,399
Asset-Backed Securities [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	103,861	60,012
Asset-Backed Securities [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	40,000
Asset-Backed Securities [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Asset-Backed Securities [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	103,861	100,012
Other Debt Securities [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	34,369	50,375
Other Debt Securities [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Other Debt Securities [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Other Debt Securities [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	34,369	50,375
Repurchase Agreements [Member] | Maturity Overnight [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	1,572,669	1,714,418
Repurchase Agreements [Member] | Maturity up to 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	58,729	88,517
Repurchase Agreements [Member] | Maturity over 90 days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	214,896	227,802
Repurchase Agreements [Member] | Total Repurchase Agreements [Member] [Domain]
Assets Sold under Agreements to Repurchase [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 1,846,294	$ 2,030,737