Borrowings - Schedule of Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Revolving Facility	$ 10,740	$ 169,579
Total borrowings	862,186	1,020,873
Less current portion	258	1,046
Less deferred debt issuance costs	2,204	4,399
Less unaccreted debt discount	936	1,193
Long-term borrowings	858,788	1,014,235
Senior Notes | 4.5% Senior Notes, due December 2020
Debt Instrument [Line Items]
Total borrowings	300,000	300,000
Senior Notes | 4.2% Senior Notes, due December 2021
Debt Instrument [Line Items]
Total borrowings	350,000	350,000
Senior Notes | 3.2% Senior Notes, due June 2023
Debt Instrument [Line Items]
Total borrowings	100,000	100,000
Senior Notes | 3.37% Senior Notes, due June 2025
Debt Instrument [Line Items]
Total borrowings	100,000	100,000
Other Borrowings
Debt Instrument [Line Items]
Other borrowings	$ 1,446	$ 1,294