Securities in an Unrealized Loss Position (Non-Investment Grade Fixed Maturity Securities) (Details) $ in Thousands	Dec. 31, 2015 USD ($) position	Dec. 31, 2014 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	$ 4,170,376	$ 2,895,204
Preferred stocks
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities | position	1
Aggregate Fair Value	$ 22,320	49,774
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	566,793	388,661
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	1,281,545	1,216,915
Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	1,309,737	583,951
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Aggregate Fair Value	$ 4,121,586	$ 2,829,501
Unrealized Loss Less than 5 Million | Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	8
Aggregate Fair Value	$ 23,370
Gross Unrealized Loss	$ 1,790
Unrealized Loss Less than 5 Million | Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	7
Aggregate Fair Value	$ 19,535
Gross Unrealized Loss	$ 264
Unrealized Loss Less than 5 Million | Residential mortgage-backed
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	12
Aggregate Fair Value	$ 128,716
Gross Unrealized Loss	$ 6,717
Unrealized Loss Less than 5 Million | State and Municipal
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	1
Aggregate Fair Value	$ 13,956
Gross Unrealized Loss	$ 3,766
Unrealized Loss Less than 5 Million | Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	28
Aggregate Fair Value	$ 185,577
Gross Unrealized Loss	$ 12,537