Summary of the Tax Effects Allocated to Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Unrealized gains on debt securities:
Reclassification adjustment for other-than-temporary impairment loss included in earnings, before tax	$ 366	$ 0
Other comprehensive income, before-tax amount	1,153
Other comprehensive income, tax (expense) or benefit	(441)
Total other comprehensive income (loss), net of tax	712	(54)
Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Unrealized gains on debt securities:
Reclassification of realized gain included in earnings	(3,122)
Less: reclassification adjustment for gain included in earnings tax (expense) or benefit	1,203
Less: reclassification adjustment for gain included in earnings net-of-tax	(1,919)
Reclassification adjustment for other-than-temporary impairment loss included in earnings, before tax	366
Reclassification adjustment for other-than-temporary impairment loss included in earnings, tax (expense) or benefit	(140)
Reclassification adjustment for other-than-temporary impairment loss included in earnings, net of tax	226
Other comprehensive income, before-tax amount	1,153
Other comprehensive income, tax (expense) or benefit	(441)
Total other comprehensive income (loss), net of tax	712
Available-for-sale Securities | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Unrealized gains on debt securities:
Unrealized gain on available-for-sale investments, before-tax amount	3,905	(88)
Unrealized gain on available-for-sale investments, tax (expense) or benefit	(1,503)	34
Unrealized gain on available-for-sale investments, net-of-tax amount	2,402	$ (54)
Restricted investments | Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Unrealized gains on debt securities:
Unrealized gain on available-for-sale investments, before-tax amount	4
Unrealized gain on available-for-sale investments, tax (expense) or benefit	(1)
Unrealized gain on available-for-sale investments, net-of-tax amount	$ 3