Income Taxes - Summary of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal income tax expense at applicable statutory rates	$ 14,843	$ 7,875	$ 17,541
Tax-exempt investment income	(230)	(272)	(586)
Dividends received deduction	(307)	(307)	(792)
Excess tax benefits on share based compensation	(1,099)	(567)	(2,114)
Effect of tax rate reduction on deferred tax liability	0	220	(3,498)
Other	99	145	(90)
Federal income tax expense	13,306	7,094	10,461
U.S. state income tax expense (benefit)	222	(86)	65
U.S. dividend withholding tax	0	0	1,053
Total income tax expense	$ 13,528	$ 7,008	$ 11,579