Significant Accounting Policies - Disaggregation of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenues
Revenue	$ 403,765	$ 393,167
ITPS
Disaggregation of Revenues
Revenue	324,580	311,937
ITPS \| United States
Disaggregation of Revenues
Revenue	250,908	269,939
ITPS \| Europe
Disaggregation of Revenues
Revenue	66,678	35,283
ITPS \| Other
Disaggregation of Revenues
Revenue	6,994	6,715
HS
Disaggregation of Revenues
Revenue	61,343	58,632
HS \| United States
Disaggregation of Revenues
Revenue	61,343	58,632
LLPS
Disaggregation of Revenues
Revenue	17,842	22,598
LLPS \| United States
Disaggregation of Revenues
Revenue	$ 17,842	$ 22,598

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration