Revenue - Balance Sheet, Cumulative Effect (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Accounts receivable, net	$ 241,841	$ 244,518	$ 244,416
Other current assets	44,623	40,171	41,799
Deferred tax assets		43,617
Other assets	37,393	23,566	15,504
Liabilities
Deferred revenue	60,547	55,738	55,738
Noncurrent contingent and other liabilities	7,179	29,292	28,801
Stockholders' equity:
Retained earnings	406,247	$ 407,218	402,544
Amounts in Accordance with ASC 606
Assets
Accounts receivable, net	241,841
Other current assets	44,623
Deferred tax assets	39,449
Other assets	37,393
Liabilities
Deferred revenue	60,547
Noncurrent contingent and other liabilities	7,179
Stockholders' equity:
Retained earnings	$ 406,247
December 31, 2017
Assets
Accounts receivable, net			244,416
Other current assets			41,799
Deferred tax assets			45,083
Other assets			15,504
Liabilities
Deferred revenue			55,833
Noncurrent contingent and other liabilities			28,801
Stockholders' equity:
Retained earnings			402,544
ASC 606 Adjustments | Amounts in Accordance with ASC 606
Assets
Accounts receivable, net			102
Other current assets			(1,628)
Deferred tax assets			(1,466)
Other assets			8,062
Liabilities
Deferred revenue			(95)
Noncurrent contingent and other liabilities			491
Stockholders' equity:
Retained earnings			$ 4,674