Summary of Significant Accounting Policies and Basis of Presentation - Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Contract receivables from billed revenue	$ 36,058								$ 43,878	$ 36,058
Contract receivables from unbilled revenue	2,709								2,987	2,709
Change in contract receivables from unbilled revenue									992	469	$ 509
Deferred revenue	(1,431)								(2,428)	(1,431)
Change in deferred revenue									(1,036)	(101)	5
Refund liabilities	7,864								6,497	7,864
Revenue, net of refund liabilities	$ 49,633	$ 43,320	$ 42,102	$ 36,721	$ 47,074	$ 42,467	$ 38,510	$ 33,569	171,776	$ 161,620	$ 140,844
Increase in revenue									10,200
Previously deferred revenue recognized during period									1,200
ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in contract receivables from billed revenue									7,820
Change in deferred revenue									(997)
Change in refund liabilities									(1,367)
Change due to adoption of ASU 2014-09 | ASU 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in contract receivables from unbilled revenue									278
C&CA
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in revenue									2,900
Lavante
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in revenue									$ 300