Investments - Fixed-maturity Securities Classified by Contractual Maturity Date (Details) - USD ($) $ in Thousands	Sep. 30, 2016		Dec. 31, 2015	[2]
Available-for-sale Securities, Debt Maturities [Abstract]
Due in one year or less, amortized cost	$ 94,127
Due after one year through five years, amortized cost	690,909
Due after five years through 10 years, amortized cost	594,927
Due after 10 years, amortized cost	47,840
Total fixed-maturity securities with single maturity dates, amortized cost	1,427,803
Mortgage and asset-backed securities, amortized cost	232,544
Available-for-sale debt securities, amortized cost basis	1,660,347	[1]	$ 1,690,043
Due in one year or less, fair value	95,946
Due after one year through five years, fair value	734,979
Due after five years through 10 years, fair value	632,004
Due after 10 years, fair value	54,401
Total fixed-maturity securities with single maturity dates, fair value	1,517,330
Mortgage and asset-backed securities, fair value	243,844
Available-for-sale debt securities, at fair value	$ 1,761,174	[1]	$ 1,731,459

[1] Includes approximately $0.1 million of other-than-temporary impairment (“OTTI”) losses related to corporates and mortgage- and asset-backed securities recognized in accumulated other comprehensive income.

[2] Includes approximately $0.1 million of OTTI related to corporates and mortgage- and asset-backed securities recognized in accumulated other comprehensive income.