Summary of Significant Accounting Policies (Significant Changes in Contract Liabilities) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Deferred revenue
January 1, 2018	$ 1,740	$ 2,218
Cash receipts (Payments)	3,296	13,803
Less: Impact on Revenue	4,872	15,857
Other	(3)	(3)
June 30, 2018	161	161
Payables to customers related to BTC
January 1, 2018	150,776	0
Cash receipts (Payments)	(109,841)	(109,841)
Less: Impact on Revenue	0	(144,944)
Other	0	5,832
June 30, 2018	40,935	40,935
Total
January 1, 2018	152,516	2,218
Cash receipts (Payments)	(106,545)	(96,038)
Less: Impact on Revenue	4,872	(129,087)
Other	(3)	5,829
June 30, 2018	$ 41,096	$ 41,096