Financial Instruments (Schedule of Long-Term Debt) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 484,584	$ 265,096
Less: current portion	(51,666)	(16)
Long-term debt, net of current portion	432,918	265,080
Private Placement, Notes [Member]
Debt Instrument [Line Items]
Long-term debt	$ 50,000	50,000
Interest rate	6.84%
Maturity date range, end	Dec. 31, 2017
Revolving Credit Agreement [Member]
Debt Instrument [Line Items]
Long-term debt	$ 418,000	$ 215,000
Interest rate at end of period	2.58%	2.27%
Capital Lease Obligations [Member]
Debt Instrument [Line Items]
Long-term debt	$ 16,584	$ 96
Interest rate	5.00%
Maturity date range, end	Dec. 31, 2022