Summary of Significant Accounting Policies - Changes by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	$ (1,845)
Cumulative credit risk adjustment	(9,211)	$ 0	$ 0
Amounts reclassified to net income	4,323
Change in net unrealized gain (loss)	4,783
Other comprehensive income (loss)	9,106
End of period	(1,950)	(1,845)
Other-than-temporary impairment losses	1,800
(Loss) gain on extinguishment of debt	104	(55,360)	$ 0
Foreign currency translation
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(553)
Cumulative credit risk adjustment	0
Amounts reclassified to net income	0
Change in net unrealized gain (loss)	(1,397)
Other comprehensive income (loss)	(1,397)
End of period	(1,950)	(553)
Unrealized loss on investment securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	(1,292)
Cumulative credit risk adjustment	0
Amounts reclassified to net income	2,802
Change in net unrealized gain (loss)	(1,510)
Other comprehensive income (loss)	1,292
End of period	0	(1,292)
Other-than-temporary impairment losses	1,800
Realized losses on investments	1,000
Redemption Note
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning of period	0
Cumulative credit risk adjustment	(9,211)
Amounts reclassified to net income	1,521
Change in net unrealized gain (loss)	7,690
Other comprehensive income (loss)	9,211
End of period	0	$ 0
(Loss) gain on extinguishment of debt	$ 1,500