Accrued Liabilities and Other Long Term Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accrued Liabilities, Current [Abstract]
Accrued expenses	$ 27,384	$ 23,159
Compensation and payroll taxes	19,423	22,414
Equipment purchases	8,563	7,395
Accrued pricing adjustments	2,328	2,891
Accrued professional services	1,978	2,215
Other	760	2,610
Accrued Liabilities, Current, Total	60,436	60,684
Liabilities, Noncurrent [Abstract]
Accrued defined benefit plan	37,618	32,749
Unrecognized tax benefits, net	15,425	20,710
Income tax contingencies	10,210	9,829
Deferred compensation	4,978	3,535
Other	10,701	12,043
Liabilities, Noncurrent, Total	$ 78,932	$ 78,866