Summary of Significant Accounting Policies - Narrative (Details) $ in Thousands		3 Months Ended
	Jan. 01, 2018 USD ($)	Mar. 31, 2018 USD ($) class_business state	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Number of business classes | class_business		2
Number of states in which entity operates | state		50
Ownership percentage		50.00%
Cumulative effect of adoption of ASU No. 2018-02, net of taxes		$ 0
Accounting Standards Update 2016-01
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle			$ 0
Deferred income taxes	$ 500
Accumulated deficit
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of adoption of ASU No. 2018-02, net of taxes		(77)
Accumulated deficit | Accounting Standards Update 2016-01
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle	1,100		556
Accumulated Other Comprehensive Income (Loss)
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of adoption of ASU No. 2018-02, net of taxes		$ 77
Accumulated Other Comprehensive Income (Loss) | Accounting Standards Update 2016-01
Schedule of Available-for-sale Securities [Line Items]
Cumulative effect of new accounting principle	$ (1,100)		$ (556)	$ 0