Revenue Recognition - Contracts with Customer (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Contract Assets
January 1, 2019 balance		$ 35
Additions		3,510
Deductions		(3,545)
June 30, 2019 balance	$ 0	0
Unbilled receivables, current
January 1, 2019 balance		1,916
Additions		2,758
Deductions		(2,338)
June 30, 2019 balance	2,336	2,336
Unbilled receivables, non-current (2)
January 1, 2019 balance		786
Additions		0
Deductions		(786)
June 30, 2019 balance	0	0
Contract Costs (2)
January 1, 2019 balance		42
Additions		0
Deductions		(38)
June 30, 2019 balance	4	4
Contract Liabilities: Deferred Revenue
January 1, 2019 balance		8,288
Additions		6,386
Deductions		(5,574)
June 30, 2019 balance	9,100	9,100
Change in Contract with Customer, Liability [Abstract]
Performance obligations satisfied	1,367	3,752
Changes in the estimated transaction price allocated to performance obligations satisfied in prior periods	(92)	43
Performance obligations satisfied from new activities in the period - contract revenue	11,044	24,106
Total revenue	$ 12,319	$ 27,901