Resale and Repurchase Agreements Schedule of Underlying Assets of Repurchase Agreements (Details) $ in Thousands	Dec. 31, 2015 USD ($)
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	$ 210,346
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	356,970
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	579,974
Maturity Overnight [Member] | Asset-backed Securities [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	212,000
Maturity Overnight [Member] | Repurchase Agreements [Member]
Schedule of Underlying Assets of Repurchase Agreements [Line Items]
Assets Sold under Agreements to Repurchase, Repurchase Liability	1,359,290
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	0
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
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	2,292
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	45,000
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	47,292
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	300,000
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	24,096
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	225,904
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
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	550,000
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	510,346
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	381,066
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	808,170
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	257,000
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	$ 1,956,582