Derivatives and Hedging Activities - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Net of tax effect on unrealized gain on derivatives	$ 1,800	$ 900
Percentage of option to prepay in equity offerings	40.00%
Period of option to prepay using proceeds from equity offering	180 days
Percentage of principal amount outstanding	50.00%
Redemption price percentage	108.25%
Other Noncurrent Liabilities
Derivative [Line Items]
Fair value of embedded derivative liability	$ 0	13,200
Other Operating Income (Expense)
Derivative [Line Items]
Change in fair value in amount included as other income (expense)	13,200	7,100
Designated as Hedging Instrument | Foreign Exchange Contract
Derivative [Line Items]
Notional foreign exchange contract outstanding		88,000
Loss recognized	3,000
Net of tax effect on unrealized gain on derivatives	(1,800)	900
Loss recognized in income, ineffective portion	200
Gain recognized		1,500
Designated as Hedging Instrument | Foreign Exchange Contract | Other Noncurrent Assets
Derivative [Line Items]
Fair value asset of derivative instrument	$ 2,400	2,400
Designated as Hedging Instrument | Foreign Exchange Contract | Other Operating Income (Expense)
Derivative [Line Items]
Gain recognized		$ 100
Senior Secured Notes Due 2021
Derivative [Line Items]
Percentage of option to prepay principal amount (equal to)	100.00%