Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Dec. 31, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Cash and cash equivalents	$ 664	$ 1,602	$ 869	$ 233
Cash Convertible Notes Hedges [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	48,361
Purchases of Level 3 instruments	0
Settlements of Level 3 instruments	0
Gains (Losses) included in Earnings	34,084
Balance at end of period	82,445
Prior Credit Agreement [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Debt Instrument, Fair Value	68,300
Debt Instrument, Carrying Amount	68,300
Cash Convertible Notes [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Debt Instrument, Fair Value	226,900
Debt Instrument, Carrying Amount	139,800
Aggregate principal of convertible notes	150,000
Cash Conversion Derivative [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	(48,361)
Purchases of Level 3 instruments	0
Settlements of Level 3 instruments	0
Gains (Losses) included in Earnings	(34,084)
Balance at end of period	(82,445)
Recurring [Member] | Cash Convertible Notes Hedges [Member] | Level 3 [Member]
Assets measured at fair value on a recurring basis
Fair Value	82,445	48,361
Recurring [Member] | Cash Conversion Derivative [Member] | Level 3 [Member]
Liabilities measured at fair value on a recurring basis
Fair Value	$ 82,445	$ 48,361