v3.8.0.1
Investments - Fair Value and Unrealized Losses (Details)
$ in Thousands
Sep. 30, 2017
USD ($)
security
Dec. 31, 2016
USD ($)
security
Fixed maturities, Fair value    
Less than 12 Months, Fair value $ 887,309 $ 1,674,889
12 Months or More, Fair value 672,040 431,159
Total, Fair value 1,559,349 2,106,048
Fixed maturities, Unrealized losses    
Less than 12 months, Unrealized losses (11,203) (29,738)
12 months or more, Unrealized losses (21,804) (57,444)
Total, Unrealized losses $ (33,007) $ (87,182)
Number of securities in an unrealized loss position | security 148 251
Investments fair value $ 1,559,349 $ 2,106,048
Investments, unrealized losses $ 33,007 $ 87,182
Number of securities in an unrealized loss position for 12 months or greater | security 93 91
Investments fair value, unrealized loss position for 12 months or greater $ 672,040 $ 431,159
Investments in unrealized loss position for 12 months or greater, unrealized losses 21,804 57,444
U.S. treasury bonds [Member]    
Fixed maturities, Fair value    
Less than 12 Months, Fair value 0 589
12 Months or More, Fair value 592 0
Total, Fair value 592 589
Fixed maturities, Unrealized losses    
Less than 12 months, Unrealized losses 0 (11)
12 months or more, Unrealized losses (8) 0
Total, Unrealized losses (8) (11)
U.S. agency bonds – mortgage-backed [Member]    
Fixed maturities, Fair value    
Less than 12 Months, Fair value 700,173 997,943
12 Months or More, Fair value 390,211 47,969
Total, Fair value 1,090,384 1,045,912
Fixed maturities, Unrealized losses    
Less than 12 months, Unrealized losses (5,545) (14,440)
12 months or more, Unrealized losses (6,906) (2,825)
Total, Unrealized losses (12,451) (17,265)
Non-U.S. government and supranational bonds [Member]    
Fixed maturities, Fair value    
Less than 12 Months, Fair value 12,678 3,169
12 Months or More, Fair value 15,132 25,236
Total, Fair value 27,810 28,405
Fixed maturities, Unrealized losses    
Less than 12 months, Unrealized losses (1,116) (160)
12 months or more, Unrealized losses (896) (5,137)
Total, Unrealized losses (2,012) (5,297)
Asset-backed securities [Member]    
Fixed maturities, Fair value    
Less than 12 Months, Fair value 21,499 30,589
12 Months or More, Fair value 3,323 0
Total, Fair value 24,822 30,589
Fixed maturities, Unrealized losses    
Less than 12 months, Unrealized losses (105) (69)
12 months or more, Unrealized losses (59) 0
Total, Unrealized losses (164) (69)
Corporate bonds [Member]    
Fixed maturities, Fair value    
Less than 12 Months, Fair value 152,959 642,599
12 Months or More, Fair value 262,782 357,954
Total, Fair value 415,741 1,000,553
Fixed maturities, Unrealized losses    
Less than 12 months, Unrealized losses (4,437) (15,058)
12 months or more, Unrealized losses (13,935) (49,482)
Total, Unrealized losses $ (18,372) $ (64,540)