Other Income (Expense) - Summary (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investment income, net
Interest and dividend income	$ 1,802	$ 4,445	$ 7,025	$ 13,016
Accretion income	218	375	641	1,696
Net realized gain (loss) on the sale of investments	125	(104)	(961)	10,757
Other-than-temporary impairment loss	(1,660)		(1,723)
Other-than-temporary impairment loss		(403)		(769)
Unrealized (loss) gain on investments, net	(89)		641
Interest income from investments in SPEs	2,049	2,050	6,148	6,151
Interest accrued on notes receivable and other interest	130	89	450	259
Total investment income, net	2,575	6,452	12,221	31,110
Interest expense
Interest expense and amortization of discount and issuance costs for Senior Notes issued by SPE	(2,197)	(2,195)	(6,590)	(6,582)
Other interest expense	(729)	(843)	(2,315)	(2,535)
Total interest expense	(2,926)	(3,038)	(8,905)	(9,117)
Other income (expense), net
Accretion income from retained interest investments	316	279	909	813
Miscellaneous (expense) income, net	(48)	304	(122)	3,833
Other income, net	268	583	787	4,646
Total other (expense) income, net	$ (83)	$ 3,997	$ 4,103	$ 26,639