Debt - 2015 Credit Agreement (Details Textual) - USD ($)	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Debt Instrument [Line Items]
Proceeds from long-term debt	$ 150,000,000
Cash used for repayment of debt	125,625,000	$ 11,250,000
Deferred financing costs related to convertible notes	5,900,000
Amortization expenses of deferred financing costs included in Interest expense	900,000
2015 Credit Agreement
Debt Instrument [Line Items]
Credit Agreement	350,000,000
Cash used for repayment of debt	120,000,000
Increase (decrease) in available cash	30,000,000
Financing cost	2,700,000
2015 Credit Agreement | Revolving Loan
Debt Instrument [Line Items]
Credit Agreement	200,000,000
2015 Credit Agreement | Term Loan
Debt Instrument [Line Items]
Credit Agreement	150,000,000
Proceeds from long-term debt	$ 150,000,000