Debt Obligations (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Oct. 30, 2014 USD ($) $ / shares	Apr. 09, 2014 USD ($)	Aug. 18, 2011 USD ($)
Debt Instrument [Line Items]
Debt Instrument, Convertible, Carrying Amount of Equity Component				$ 66,100
Term Loan, Due 2016	$ 60,000	$ 67,031
Revolving Credit Agreements, due 2016	159,963	7,701
Line of Credit Facility, Fair Value of Amount Outstanding	219,963	74,732
Convertible Debt	358,293	347,878
Total Debt Obligations	602,148	428,341
Unamortized Debt Issuance Expense	(8,324)	(10,809)
Carrying value of debt	593,824	417,532
Long-term Debt, Current Maturities	(32,161)	(12,060)
Long-term Debt, Excluding Current Maturities	561,663	$ 405,472
Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months	9,000
Long-term Debt, Maturities, Repayments of Principal in Year Two	14,200
Long-term Debt, Maturities, Repayments of Principal in Year Three	197,500
Long-term Debt, Maturities, Repayments of Principal in Year Four	$ 402,500
Line of Credit Facility, Maximum Borrowing Capacity					$ 675,000
Long-term Debt, Weighted Average Interest Rate	2.15%	1.80%
Line of Credit Facility, Interest Rate at Period End	2.40%	10.10%
Debt Instrument, Interest Rate Terms	The base rate is the highest of (i) the Bank of America prime rate, (ii) the Federal Funds rate plus 0.50% or (iii) the Fixed LIBOR rate plus 1.00%.
Letter of credit, interest rate at period end	1.38%
Letters of Credit Outstanding, Amount	$ 68,200
Debt Instrument, Convertible, Conversion Price | $ / shares				$ 72.18
Debt Instrument, Face Amount				$ 402,500
Other debt obligations	23,892	$ 5,731
Other debt, current	23,300
Long-term Debt, Maturities, Repayments of Principal after Year Five	0
1.5% Issue [Member]
Debt Instrument [Line Items]
Debt Issuance Costs, Gross				$ 10,700
Debt Instrument, Interest Rate, Stated Percentage				1.50%
Debt Instrument, Unamortized Discount	44,200	54,600
Amortization of Debt Discount (Premium)	10,400	$ 9,900	$ 1,600
Debt Instrument, Convertible, Effective Interest Rate		4.70%
Debt Instrument, Convertible, Interest Expense	6,000	$ 6,000	$ 900
Term Loan [Member]
Debt Instrument [Line Items]
Term Loan, Due 2016					$ 75,000
Line of Credit [Member]
Debt Instrument [Line Items]
Letters of Credit Outstanding, Amount	$ 44,900	$ 42,000
Line of credit - India [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity						$ 10,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity						$ 590,000
Minimum [Member]
Debt Instrument [Line Items]
Consolidated Fixed Charge Coverage Ratio	1.5
Maximum [Member]
Debt Instrument [Line Items]
Consolidated Total Leverage Ratio	4.0
Letter of Credit [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 200,000
Swingline loans [Member] | Line of Credit [Member]
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 25,000
LIBOR [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.375%
LIBOR [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.375%
Base rate [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	0.375%
Base rate [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.375%