Significant Accounting Policies - Narrative (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	May 31, 2018 USD ($) $ / shares shares	Sep. 30, 2018 USD ($) Project $ / shares shares	Sep. 30, 2017 Project	Sep. 30, 2018 USD ($) Project Source	Sep. 30, 2017 Project	Dec. 31, 2017 USD ($)	Jul. 26, 2016 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of product revenue sources | Source				2
Unbilled receivables		$ 47,300,000		$ 47,300,000		$ 41,000,000
Number of projects | Project		8	7	14	8
Percentage of total revenues		15.70%	15.00%	14.00%	15.00%
Percentage of product revenues		23.10%	20.00%	20.30%	19.00%
Number of service revenue sources | Source				2
Restructuring and other charges		$ 3,700,000		$ 3,700,000
Average price of shares (in dollars per share) | $ / shares	$ 44.87	$ 50.95
Treasury shares (at cost)		$ 71,107,000		$ 71,107,000		$ 0
Common Stock
Restructuring Cost and Reserve [Line Items]
Shares authorized to be purchased (up to) (in shares)							$ 100,000,000
Treasury shares purchased (in shares) | shares		1,395,521
Treasury stock, value of acquired shares		$ 71,100,000
Stock repurchased and retired during period (in shares) | shares	219,102
Stock repurchased and retired during period	$ 9,800,000