Fair Value of Financial Instruments - Schedule of Fair Value Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	$ 2,538,197	$ 2,464,611
Equity securities	39,638	38,023
Cash and cash equivalents	439,944	547,569
Separate account assets	2,638,901	2,659,520
Separate account liabilities	$ 2,638,901	2,659,520
Fair value assumptions, percentage of securities assessed by third-party pricing service	99.00%
Fair Value, Recurring Measurements [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	$ 2,538,197
Short-term investments	50,758
Total available-for-sale securities	2,588,955	2,464,611
Equity securities	39,638	38,023
Trading securities	35,046	16,300
Cash and cash equivalents	439,944	547,569
Separate account assets	2,638,901	2,659,520
Assets, fair value disclosure	5,742,484	5,726,023
Separate account liabilities	2,638,901	2,659,520
Liabilities, fair value disclosure	2,638,901	2,659,520
Fair Value, Recurring Measurements [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	5,810
Total available-for-sale securities	5,810	6,074
Equity securities	36,622	34,910
Cash and cash equivalents	439,944	285,074
Assets, fair value disclosure	482,376	326,058
Fair Value, Recurring Measurements [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	2,530,146
Short-term investments	50,758
Total available-for-sale securities	2,580,904	2,458,510
Equity securities	1,080	1,093
Trading securities	35,046	16,300
Cash and cash equivalents		262,495
Separate account assets	2,638,901	2,659,520
Assets, fair value disclosure	5,255,931	5,397,918
Separate account liabilities	2,638,901	2,659,520
Liabilities, fair value disclosure	2,638,901	2,659,520
Fair Value, Recurring Measurements [Member] | Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	2,241
Total available-for-sale securities	2,241	27
Equity securities	1,936	2,020
Assets, fair value disclosure	4,177	2,047
Fair Value, Recurring Measurements [Member] | U.S. Government and Agencies [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	10,061	10,144
Fair Value, Recurring Measurements [Member] | U.S. Government and Agencies [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	10,061	10,144
Fair Value, Recurring Measurements [Member] | Foreign Government [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	182,277	183,252
Fair Value, Recurring Measurements [Member] | Foreign Government [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	182,277	183,252
Fair Value, Recurring Measurements [Member] | States and Political Subdivisions [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	166,196	170,689
Fair Value, Recurring Measurements [Member] | States and Political Subdivisions [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	166,196	170,689
Fair Value, Recurring Measurements [Member] | Corporates [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	1,692,199	1,628,168
Fair Value, Recurring Measurements [Member] | Corporates [Member] | Level 1 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	5,810	6,074
Fair Value, Recurring Measurements [Member] | Corporates [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	1,684,175	1,622,094
Fair Value, Recurring Measurements [Member] | Corporates [Member] | Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	2,214
Fair Value, Recurring Measurements [Member] | Residential Mortgage-backed Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	256,326	272,741
Fair Value, Recurring Measurements [Member] | Residential Mortgage-backed Securities [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	256,299	272,714
Fair Value, Recurring Measurements [Member] | Residential Mortgage-backed Securities [Member] | Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	27	27
Fair Value, Recurring Measurements [Member] | Commercial Mortgage-backed Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	144,265	112,865
Fair Value, Recurring Measurements [Member] | Commercial Mortgage-backed Securities [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	144,265	112,865
Fair Value, Recurring Measurements [Member] | Other Asset-backed Securities [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	86,873	86,752
Fair Value, Recurring Measurements [Member] | Other Asset-backed Securities [Member] | Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Total available-for-sale fixed-maturity securities	$ 86,873	$ 86,752