Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets
Unearned premium reserve reduction	$ 11,488	$ 12,103
Compensation accruals	9,487	8,866
Reinsurance commissions	0	6,804
Impaired securities	2,127	1,245
Other comprehensive income - net funded status of benefit plans	2,981	2,875
Discounting of unpaid claims and claim expense tax reserves	2,548	2,530
Net operating loss carryforwards	0	3,803
Postretirement benefits other than pensions	270	285
Total gross deferred tax assets	28,901	38,511
Deferred tax liabilities
Other comprehensive income - net unrealized gains on securities	124,715	74,645
Deferred policy acquisition costs	36,347	49,326
Life insurance future policy benefit reserve	26,725	38,210
Life insurance future policy benefit reserve (transitional rule)	10,651	12,786
Discounting of unpaid claims and claim expense tax reserves (transitional rule)	789	947
Investment related adjustments	34,155	15,718
Intangibles	210	2,021
Other, net	1,959	5,482
Total gross deferred tax liabilities	235,551	199,135
Net deferred tax liability	$ 206,650	$ 160,624