Revenue Revenue - Balance Sheet, Cumulative Effect (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue from External Customer [Line Items]
Accounts receivable, net	$ 243,400	$ 244,518	$ 244,416
Other current assets	57,814	40,171	41,799
Deferred tax assets	44,384	43,617	45,083
Other assets	29,885	23,566	15,504
Deferred revenue	66,581	55,738	55,833
Noncurrent contingent and other liabilities	20,185	29,292	28,801
Retained earnings	407,392	$ 407,218	402,544
Amounts in Accordance with ASC 606
Revenue from External Customer [Line Items]
Accounts receivable, net	243,400
Other current assets	57,814
Deferred tax assets	44,384
Other assets	29,885
Deferred revenue	66,581
Noncurrent contingent and other liabilities	20,185
Retained earnings	$ 407,392
December 31, 2017
Revenue from External Customer [Line Items]
Accounts receivable, net			244,416
Other current assets			41,799
Deferred tax assets			45,083
Other assets			15,504
Deferred revenue			55,833
Noncurrent contingent and other liabilities			28,801
Retained earnings			402,544
ASC 606 Adjustments | Amounts in Accordance with ASC 606
Revenue from External Customer [Line Items]
Accounts receivable, net			102
Other current assets			(1,628)
Deferred tax assets			(1,466)
Other assets			8,062
Deferred revenue			(95)
Noncurrent contingent and other liabilities			491
Retained earnings			$ 4,674