Borrowings - Schedule of Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Jun. 13, 2016	Dec. 09, 2011	Dec. 06, 2010
Debt Instrument [Line Items]
Revolving Facility		$ 10,740
Total borrowings	$ 851,078	862,186
Less current portion	483	258
Less deferred debt issuance costs	1,593	2,204
Less unaccreted debt discount	667	936
Long-term borrowings	$ 848,335	$ 858,788
4.50% Senior Notes, due December 2020
Debt Instrument [Line Items]
Stated interest rate	4.50%	4.50%			4.50%
4.20% Senior Notes, due December 2021
Debt Instrument [Line Items]
Stated interest rate	4.20%	4.20%		4.20%
3.20% Senior Notes, due June 2023
Debt Instrument [Line Items]
Stated interest rate	3.20%	3.20%
3.37% Senior Notes, due June 2025
Debt Instrument [Line Items]
Stated interest rate	3.37%	3.37%
Senior Notes | 4.50% Senior Notes, due December 2020
Debt Instrument [Line Items]
Stated interest rate	4.50%
Total borrowings	$ 300,000	$ 300,000
Senior Notes | 4.20% Senior Notes, due December 2021
Debt Instrument [Line Items]
Stated interest rate	4.20%
Total borrowings	$ 350,000	350,000
Senior Notes | 3.20% Senior Notes, due June 2023
Debt Instrument [Line Items]
Stated interest rate	3.20%		3.20%
Total borrowings	$ 100,000	100,000
Senior Notes | 3.37% Senior Notes, due June 2025
Debt Instrument [Line Items]
Stated interest rate	3.37%		3.37%
Total borrowings	$ 100,000	100,000
Other Borrowings
Debt Instrument [Line Items]
Other borrowings	$ 1,078	$ 1,446