Debt - Short-Term Borrowings (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Jun. 06, 2014	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Line of Credit Facility [Line Items]
Short-term borrowings		$ 246,000		$ 246,000		$ 169,643
Interest expense, net		1,878	$ 1,217	4,988	$ 3,082
Revolving Credit Facility
Line of Credit Facility [Line Items]
Short-term borrowings		246,000		246,000		$ 169,643
Minimum
Line of Credit Facility [Line Items]
Short-term borrowings		140,000	112,292	140,000	112,292
Maximum
Line of Credit Facility [Line Items]
Short-term borrowings		$ 249,000	$ 229,782	$ 249,000	$ 229,782
Credit Agreement | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt Instrument, Term	5 years