Income Taxes - Components of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets
Unearned premium reserve reduction	$ 12,112	$ 11,472
Compensation accruals	6,866	8,359
Impaired securities	1,295	2,240
Other comprehensive income - net funded status of benefit plans	3,254	3,526
Discounting of unpaid claims and claim expense tax reserves	2,772	3,889
Postretirement benefits other than pensions	302	321
Charitable contributions carryforwards	89	62
Net operating loss carryforwards	10,969	148
Total gross deferred tax assets	37,659	30,017
Deferred tax liabilities
Other comprehensive income - net unrealized gains on securities	32,897	95,583
Deferred policy acquisition costs	60,330	52,438
Life insurance future policy benefit reserve	9,304	102
Life insurance future policy benefit reserve (transitional rule)	14,910	23,869
Discounting of unpaid claims and claim expense tax reserves (transitional rule)	1,203	2,513
Investment related adjustments	17,531	8,661
Intangibles	2,557	2,557
Other, net	2,613	2,069
Total gross deferred tax liabilities	141,345	187,792
Net deferred tax liability	$ 103,686	$ 157,775