Fair Value Level 3 Fixed Maturity Securities on a recurring basis by valuation source (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 3,708,655	$ 3,518,707
percent of total	67.30%	88.90%
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 575,954	$ 553,992
percent of total	5.60%	1.60%
Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 422,300	$ 465,506
percent of total	4.00%	3.40%
Other asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 770,650	$ 583,122
percent of total	13.20%	4.60%
United States Government and agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 32,072	$ 44,098
percent of total	0.20%	0.10%
Fair Value, Measurements, Recurring [Member] | Corporate | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 59,119	$ 49,076
Fair Value, Measurements, Recurring [Member] | United States Government and agencies | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	0	8,726
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 194,921	$ 205,268
percent of total	100.00%	100.00%
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Corporate
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 3,708,655	$ 3,518,707
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Corporate | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	59,119	49,076
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	81,434	88,180
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities		3,729
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Other asset-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	54,368	55,557
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | United States Government and agencies
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	32,072	44,098
Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | United States Government and agencies | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities		8,726
Estimate of Fair Value Measurement [Member] | Third-party Vendor [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 138,426	$ 140,808
percent of total	71.00%	68.60%
Estimate of Fair Value Measurement [Member] | Third-party Vendor [Member] | Fair Value, Measurements, Recurring [Member] | Corporate | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 17,684	$ 17,208
Estimate of Fair Value Measurement [Member] | Third-party Vendor [Member] | Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	81,434	88,180
Estimate of Fair Value Measurement [Member] | Third-party Vendor [Member] | Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities		0
Estimate of Fair Value Measurement [Member] | Third-party Vendor [Member] | Fair Value, Measurements, Recurring [Member] | Other asset-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	39,308	35,420
Estimate of Fair Value Measurement [Member] | Third-party Vendor [Member] | Fair Value, Measurements, Recurring [Member] | United States Government and agencies | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities		0
Estimate of Fair Value Measurement [Member] | Internally priced [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 56,495	$ 64,460
percent of total	29.00%	31.40%
Estimate of Fair Value Measurement [Member] | Internally priced [Member] | Fair Value, Measurements, Recurring [Member] | Corporate | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 41,435	$ 31,868
Estimate of Fair Value Measurement [Member] | Internally priced [Member] | Fair Value, Measurements, Recurring [Member] | Commercial mortgage-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	0	0
Estimate of Fair Value Measurement [Member] | Internally priced [Member] | Fair Value, Measurements, Recurring [Member] | Residential mortgage-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities		3,729
Estimate of Fair Value Measurement [Member] | Internally priced [Member] | Fair Value, Measurements, Recurring [Member] | Other asset-backed | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities	$ 15,060	20,137
Estimate of Fair Value Measurement [Member] | Internally priced [Member] | Fair Value, Measurements, Recurring [Member] | United States Government and agencies | Fair Value, Inputs, Level 3
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Available-for-sale Securities		$ 8,726