Business Ink Acquisition - Summary of Preliminary Estimated Fair Values of Assets Acquired and Liabilities Assumed at Date of Acquisition (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Feb. 28, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 222,915		$ 210,080
Business Ink
Business Acquisition [Line Items]
Current assets		$ 25,479
Fixed assets		13,337
Goodwill		8,025
Non-current assets		148
Total assets acquired		81,951
Current liabilities		(11,730)
Non-current liabilities		(256)
Total liabilities assumed		(11,986)
Net assets acquired		69,965
Client contracts | Business Ink
Business Acquisition [Line Items]
Intangible assets, Acquired		30,830
Software | Business Ink
Business Acquisition [Line Items]
Intangible assets, Acquired		$ 4,132