Revenues - Impact Of Adopting New Revenue Recognition Standard (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts and notes receivable, net	$ 116,518	$ 84,979	$ 56,064
Contract assets, net	13,263	5,512	0
Prepaid expenses and other current assets	30,514	23,699	21,696
Total current assets	524,387	114,190	205,192
Deferred income tax assets, net	18,080	10,597	15,755
Long-term notes receivable, net of current portion	38,220	23,900	36,877
Other assets	23,396	20,689	15,366
Total assets	681,695	169,376	338,112
Accrued liabilities	36,908	26,014	23,502
Contract with customer, liability, current	89,637	71,264	70,401
Total current liabilities	141,505	97,278	107,950
Deferred revenue, net of current portion	69,382	56,130	54,881
Total liabilities	222,033	153,408	170,668
Retained earnings	169,301	142,179	123,185
Total stockholders’ equity	459,662	142,179	167,444
Total liabilities and stockholders’ equity	$ 681,695	295,587	338,112
December 31, 2017 (As reported)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts and notes receivable, net			56,064
Contract assets, net			0
Prepaid expenses and other current assets			21,696
Total current assets			77,760
Deferred income tax assets, net			15,755
Long-term notes receivable, net of current portion			36,877
Other assets			15,366
Total assets			145,758
Accrued liabilities			23,502
Contract with customer, liability, current			70,401
Total current liabilities			93,903
Deferred revenue, net of current portion			54,881
Total liabilities			148,784
Retained earnings			123,185
Total stockholders’ equity			123,185
Total liabilities and stockholders’ equity			271,969
Impact of Adoption of Topic 606 on Opening Balance Sheet | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts and notes receivable, net		28,915
Contract assets, net		5,512
Prepaid expenses and other current assets		2,003
Total current assets		36,430
Deferred income tax assets, net		(5,158)
Long-term notes receivable, net of current portion		(12,977)
Other assets		5,323
Total assets		23,618
Accrued liabilities		2,512
Contract with customer, liability, current		863
Total current liabilities		3,375
Deferred revenue, net of current portion		1,249
Total liabilities		4,624
Retained earnings		18,994	$ 19,000
Total stockholders’ equity		18,994
Total liabilities and stockholders’ equity		$ 23,618