Revenues - Impact Of Adopting New Revenue Recognition Standard (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accounts and notes receivable, net	$ 94,296	$ 84,979	$ 56,064
Contract assets, net	10,468	5,512	0
Prepaid expenses and other current assets	26,604	23,699	21,696
Total current assets	486,966	114,190	205,192
Deferred income tax assets, net	15,813	10,597	15,755
Long-term notes receivable, net of current portion	37,158	23,900	36,877
Other assets	22,831	20,689	15,366
Total assets	642,397	169,376	338,112
Accrued liabilities	29,995	26,014	23,502
Current portion of deferred revenue	76,583	71,264	70,401
Total current liabilities	120,898	97,278	107,950
Deferred revenue, net of current portion	61,456	56,130	54,881
Total liabilities	193,555	153,408	170,668
Retained earnings	163,590	142,179	123,185
Total stockholders’ equity	448,842	142,179	167,444
Total liabilities and stockholders’ equity	$ 642,397	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
Current portion of deferred revenue			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
Current portion of deferred revenue		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