Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Deferred tax assets:
Other employee benefits	$ 17,781	$ 16,358
Unrealized losses on investments	7,164	15,403
Deferred revenue	3,756	3,710
Allowance for management fee returned on cancelled policies	3,571	3,405
Current expected credit loss allowance	2,661	1,112
Other	3,709	2,790
Total deferred tax assets	38,642	42,778
Deferred tax liabilities:
Depreciation	31,126	37,682
Pension and other postretirement benefits	14,738	15,473
Prepaid expenses	2,001	1,731
Other	2,258	1,967
Total deferred tax liabilities	50,123	56,853
Net deferred tax liability	$ (11,481)	$ (14,075)