Investments - Additional Information (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) Issue	Sep. 30, 2017 USD ($)	Dec. 31, 2017 Issue
Gain (Loss) on Securities [Line Items]
Total issues of fixed maturity portfolio | Issue	1,538		1,502
Fixed Maturities [Member]
Gain (Loss) on Securities [Line Items]
Other than-temporary impairment, available for sale securities	$ 0	$ 245,000
Other-than-temporary impairment, available for sale securities, net of tax		$ 159,000