Basis of Presentation and Summary of Significant Accounting Policies - Summary of Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Contract assets:
Beginning balance	$ 1,956	$ 739	$ 739
Additions	991		7,117
Deductions	(320)		(5,900)
Ending balance	2,627		1,956
Contract liabilities:
Beginning balance	1,280	100	100
Additions	1,145		4,428
Deductions	(1,104)		(3,248)
Ending balance	1,321		$ 1,280
Reclassified from unbilled revenue to accounts receivable	(300)
Reclassified from deferred revenue to revenue	$ (1,100)	$ (3,200)