Accumulated Other Comprehensive Loss - Summary of the Tax Effects Allocated to Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Loss
Reclassification adjustment for loss (gain) included in earnings, Before-tax-amount		$ 1,061	$ (10,750)	$ (795)
Reclassification of other-than-temporary impairment loss included in earnings, Before-tax-amount		2,330	2,288
Reclassification into retained earnings for the adoption of ASU, Before-tax-amount	[1]	932
Total before income taxes		1,472	(6,456)	5,196
Other comprehensive loss, Tax (expense) or benefit	[2]	(685)	2,488	(2,003)
Total other comprehensive income (loss), net of tax		787	(3,968)	$ 3,193
Unrealized (loss) gain on investments
Accumulated Other Comprehensive Loss
Unrealized (loss) gain on investments, Net-of-tax amount		(2,127)	1,235
Reclassification adjustment for loss (gain) included in earnings, Before-tax-amount		1,061	(10,750)
Reclassification adjustment for loss (gain) included in earnings, Tax (expense) or benefit		(269)	4,139
Reclassification adjustment for loss (gain) included in earnings, Net-of-tax amount		792	(6,611)
Reclassification of other-than-temporary impairment loss included in earnings, Before-tax-amount		2,330	2,288
Reclassification adjustment for other-than-temporary impairment loss included in earnings, Tax (expense) or benefit		(592)	(880)
Reclassification adjustment for other-than-temporary impairment loss included in earnings, Net-of-tax amount		1,738	1,408
Total before income taxes		1,472	(6,456)
Other comprehensive loss, Tax (expense) or benefit		(685)	2,488
Total other comprehensive income (loss), net of tax		787	(3,968)
Unrealized (loss) gain on investments | ASU 2016-01
Accumulated Other Comprehensive Loss
Reclassification into retained earnings for the adoption of ASU, Before-tax-amount		932
Reclassification into retained earnings for the adoption of ASU, Tax (expense) or benefit		(236)
Reclassification into retained earnings for the adoption of ASU, Net-of-tax amount		696
Unrealized (loss) gain on investments | ASU 2018-02
Accumulated Other Comprehensive Loss
Reclassification into retained earnings for the adoption of ASU, Tax (expense) or benefit		(313)
Reclassification into retained earnings for the adoption of ASU, Net-of-tax amount		(313)
Unrestricted available-for-sale, Debt securities | Unrealized (loss) gain on investments
Accumulated Other Comprehensive Loss
Unrealized (loss) gain on investments, Before-tax amount		(2,845)	2,015
Unrealized (loss) gain on investments, Tax (expense) or benefit		723	(774)
Unrealized (loss) gain on investments, Net-of-tax amount		(2,122)	1,241
Restricted | Unrealized (loss) gain on investments
Accumulated Other Comprehensive Loss
Unrealized (loss) gain on investments, Before-tax amount		(6)	(9)
Unrealized (loss) gain on investments, Tax (expense) or benefit		2	3
Unrealized (loss) gain on investments, Net-of-tax amount		$ (4)	$ (6)

[1] The reclassification into retained earnings relates to the adoption of ASU 2016-01. The new guidance was effective January 1, 2018, and required equity investments to be measured at fair value with changes in fair value recognized in results of operations rather than the consolidated statements of comprehensive income. See Note 2. Summary of Significant Accounting Policies.

[2] Income tax expense for the year ended December 31, 2018 includes $0.3 million of income tax expense related to the adoption of ASU 2018-02. The new guidance was effective January 1, 2018, and allowed a reclassification from accumulated other comprehensive loss to retained earnings for stranded tax effects resulting from the Tax Act. See Note 2. Summary of Significant Accounting Policies.