Revenue Revenue - Balance Sheet, Impact of Adoption (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
Amounts in Accordance with ASC 605
Revenue from External Customer [Line Items]
Accounts receivable, net	240,814
Other current assets	59,243
Deferred tax assets	46,145
Other assets	21,837
Deferred revenue	66,735
Noncurrent contingent and other liabilities	19,798
Retained earnings	400,181
Difference between Revenue Guidance in Effect before and after Topic 605, 606 [Member] | Effect of change higher (lower)
Revenue from External Customer [Line Items]
Accounts receivable, net	2,586
Other current assets	(1,429)
Deferred tax assets	(1,761)
Other assets	8,048
Deferred revenue	(154)
Noncurrent contingent and other liabilities	387
Retained earnings	$ 7,211