Income Taxes - Reconciliation of Effective Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Expected federal tax on income	$ 4,103	$ 31,041	$ 39,981
Add (deduct) tax effects of:
Tax-exempt interest	(3,726)	(5,335)	(5,789)
Dividend received deduction	(412)	(4,810)	(5,751)
Tax Act DTL re-measurement	0	(98,988)	0
Employee share-based compensation	(1,134)	(3,258)	127
Compensation deduction limitation	1,754	326	0
Prior year adjustments	300	(293)	91
Other, net	309	545	1,808
Total income tax expense (benefit)	$ 1,194	$ (80,772)	$ 30,467