Resale and Repurchase Agreements Schedule of Underlying Assets of Repurchase Agreements (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Maturity Overnight [Member] | US Treasury and Government [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 387,541	$ 271,820
Maturity Overnight [Member] | US Government-sponsored Enterprise Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	18,466	149,111
Maturity Overnight [Member] | Agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	882,744	737,975
Maturity Overnight [Member] | Non-agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	187,740	0
Maturity Overnight [Member] | Asset-backed Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	322,680	89,601
Maturity Overnight [Member] | Other Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	98,522	14,780
Maturity Overnight [Member] | Repurchase Agreements [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	1,897,693	1,263,287
Maturity up to 90 days [Member] | US Treasury and Government [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	150,000	1,731
Maturity up to 90 days [Member] | US Government-sponsored Enterprise Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity up to 90 days [Member] | Agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	31,774	9,750
Maturity up to 90 days [Member] | Non-agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity up to 90 days [Member] | Asset-backed Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	30,000
Maturity up to 90 days [Member] | Other Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity up to 90 days [Member] | Repurchase Agreements [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	181,774	41,481
Maturity Greater than 90 Days [Member] | US Treasury and Government [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	100,000	450,000
Maturity Greater than 90 Days [Member] | US Government-sponsored Enterprise Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity Greater than 90 Days [Member] | Agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	213,752	200,000
Maturity Greater than 90 Days [Member] | Non-agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity Greater than 90 Days [Member] | Asset-backed Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity Greater than 90 Days [Member] | Other Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	0	0
Maturity Greater than 90 Days [Member] | Repurchase Agreements [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	313,752	650,000
Total Repurchase Agreements [Member] [Domain] | US Treasury and Government [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	637,541	723,551
Total Repurchase Agreements [Member] [Domain] | US Government-sponsored Enterprise Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	18,466	149,111
Total Repurchase Agreements [Member] [Domain] | Agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	1,128,270	947,725
Total Repurchase Agreements [Member] [Domain] | Non-agency mortgage-backed securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	187,740	0
Total Repurchase Agreements [Member] [Domain] | Asset-backed Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	322,680	119,601
Total Repurchase Agreements [Member] [Domain] | Other Debt Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	98,522	14,780
Total Repurchase Agreements [Member] [Domain] | Repurchase Agreements [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	$ 2,393,219	$ 1,954,768