Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets—
Accounts receivable and allowance for doubtful accounts	$ 1,445	$ 715
Stock-based compensation	2,538	2,297
Accrued liabilities and expenses	19,449	19,555
Net operating loss carryforwards	3,242	6,007
Intangible assets	5,071	2,272
Other	550	544
Subtotal	32,295	31,390
Valuation allowances	(648)	(3,500)
Total deferred tax assets	31,647	27,890
Deferred tax liabilities—
Property and equipment	(10,488)	(4,668)
Long-term contracts	(688)	(625)
Goodwill	(3,864)	(1,572)
Other	(360)	(322)
Total deferred tax liabilities	(15,400)	(7,187)
Net deferred tax assets	16,247	20,703
Deferred income tax assets
Deferred income tax assets	17,634	22,966
Deferred income tax liabilities
Deferred tax liabilities	$ 1,387	$ 2,263