Borrowings Components of long-term debt (Details) - USD ($) $ in Thousands	Jun. 28, 2015	Jun. 01, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Revolving credit facility, at a rate of 1.94% at June 28, 2015, due 2018	$ 446,000		$ 200,000
Total borrowings	1,141,717		1,104,598
Less: Unamortized debt discount on 3.875% Convertible Senior Subordinated Notes due 2017	(29,726)		(36,197)
Total long-term debt	1,111,991		1,068,401
Current borrowings	(415,991)		(368,401)
Long-term borrowings	696,000		700,000
3.875% Convertible Senior Subordinated Notes
Debt Instrument [Line Items]
3.875% Convertible Senior Subordinated Notes due 2017	399,817		399,898
6.875% Senior Subordinated Notes due 2019
Debt Instrument [Line Items]
6.875% Senior Subordinated Notes due 2019	0	$ 250,000	250,000
5.25% Senior Subordinated Notes Due 2024
Debt Instrument [Line Items]
5.25% Senior Notes due 2024	250,000		250,000
Securitization Program
Debt Instrument [Line Items]
Securitization program, at a rate of 0.94% at June 28, 2015	$ 45,900		$ 4,700