Fair Value Valuation of our Financial Instruments Measured on a Recurring Basis by Hierarchy Levels (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	$ 16,145	$ 9,518
Assets held in separate accounts	597,072	625,257
Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	11,272	2,331
Cash, cash equivalents and short-term investments	49,931	57,741
Reinsurance recoverable	3,411	2,636
Assets held in separate accounts	597,072	625,257
Future policy benefits-index annuity embedded derivatives	3,903,177	3,618,145
Other liabilities	114	56
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities		56
Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	9,360	2,331
Cash, cash equivalents and short-term investments	49,931	57,741
Reinsurance recoverable	3,411	2,636
Assets held in separate accounts	597,072	625,257
Assets, Fair Value Disclosure	7,801,532	7,447,408
Future policy benefits-index annuity embedded derivatives	15,778	9,374
Other liabilities	114
Liabilities, Fair Value Disclosure	15,892	9,430
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Cash, cash equivalents and short-term investments	49,931	57,741
Reinsurance recoverable	0	0
Assets held in separate accounts	597,072	625,257
Future policy benefits-index annuity embedded derivatives	0	0
Other liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	662,002	702,486
Liabilities, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	9,360	2,331
Cash, cash equivalents and short-term investments	0	0
Reinsurance recoverable	3,411	2,636
Assets held in separate accounts	0	0
Future policy benefits-index annuity embedded derivatives	0	0
Other liabilities	114	56
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure	6,937,198	6,532,183
Liabilities, Fair Value Disclosure	114	56
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other investments	0	0
Cash, cash equivalents and short-term investments	0	0
Reinsurance recoverable	0	0
Assets held in separate accounts	0	0
Future policy benefits-index annuity embedded derivatives		9,374
Other liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	194,921	205,268
Assets, Fair Value Disclosure	202,332	212,739
Liabilities, Fair Value Disclosure	15,778	9,374
Corporate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	3,708,655	3,518,707
Corporate | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	3,708,655	3,518,707
Corporate | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Corporate | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	3,649,536	3,469,631
Corporate | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	59,119	49,076
Corporate | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	59,119	49,076
Residential mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	422,300	465,506
Residential mortgage-backed | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	422,300	465,506
Residential mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	0	0
Residential mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	422,300	461,777
Residential mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	0	3,729
Residential mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		3,729
Commercial mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	575,954	553,992
Commercial mortgage-backed | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	575,954	553,992
Commercial mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	0	0
Commercial mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	494,520	465,812
Commercial mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	81,434	88,180
Commercial mortgage-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	81,434	88,180
Other asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	770,650	583,122
Other asset-backed | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	770,650	583,122
Other asset-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	0	0
Other asset-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	716,282	527,565
Other asset-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Mortgage-backed Securities Available-for-sale, Fair Value Disclosure	54,368	55,557
Other asset-backed | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	54,368	55,557
United States Government and agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	32,072	44,098
United States Government and agencies | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	32,072	44,098
United States Government and agencies | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	11,943	14,760
United States Government and agencies | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	20,129	20,612
United States Government and agencies | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	8,726
United States Government and agencies | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities		8,726
State, municipal and other governments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	1,499,159	1,472,351
State, municipal and other governments | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	1,499,159	1,472,351
State, municipal and other governments | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
State, municipal and other governments | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	1,499,159	1,472,351
State, municipal and other governments | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Non-redeemable preferred stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	102,417	91,951
Non-redeemable preferred stocks | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	102,417	91,951
Non-redeemable preferred stocks | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	0	0
Non-redeemable preferred stocks | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	95,006	84,480
Non-redeemable preferred stocks | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	7,411	7,471
Common stocks
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	30,551	29,716
Common stocks | Fair Value, Measurements, Recurring [Member] | Estimate of Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	30,551	29,716
Common stocks | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	3,056	4,728
Common stocks | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	27,495	24,988
Common stocks | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale Securities	$ 0	$ 0