Other Income (Expense) - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Investment income, net
Interest and dividend income	$ 2,342	$ 4,024	$ 5,222	$ 8,572
Accretion income	202	399	423	1,320
Net realized (loss) gain on the sale of investments	(8)	7,739	(1,086)	10,861
Other-than-temporary impairment loss			(63)
Other-than-temporary impairment loss				(366)
Unrealized gain on investments, net	1,267		729
Interest income from investments in SPEs	2,049	2,050	4,099	4,101
Interest accrued on notes receivable and other interest	129	91	322	170
Total investment income, net	5,981	14,303	9,646	24,658
Interest expense
Interest expense and amortization of discount and issuance costs for Senior Notes issued by SPE	(2,197)	(2,194)	(4,393)	(4,387)
Other interest expense	(757)	(841)	(1,586)	(1,691)
Total interest expense	(2,954)	(3,035)	(5,979)	(6,078)
Other income (expense), net
Accretion income from retained interest investments	303	271	593	534
Miscellaneous (expense) income, net	(60)	57	(73)	3,529
Other income, net	243	328	520	4,063
Total other income, net	$ 3,270	$ 11,596	$ 4,187	$ 22,643