Debt - 2010 Convertible Notes (Details Textual) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2016	Mar. 31, 2010
Debt Instrument [Line Items]
Convertible notes cash paid			$ 215,676,000
Senior Subordinated Convertible Notes 2010
Debt Instrument [Line Items]
Senior subordinated convertible notes face amount				$ 150,000,000
Interest rate on senior subordinated convertible notes				3.00%
Maturity period		Mar. 01, 2017
Aggregate principal amount of convertible notes repurchased			115,300,000
Amount paid to purchase aggregate principal amount			215,600,000
Loss on repurchase of convertible notes			8,700,000
Convertible notes cash paid	$ 34,800,000
Settlement of conversion obligation by common shares delivered from treasury stock	694,240
Settlement of conversion obligation in excess of par value	$ 28,800,000
2010 Convertible Notes Converted by Holders
Debt Instrument [Line Items]
Aggregate principal amount of convertible notes repurchased			50,000
Amount paid to purchase aggregate principal amount			$ 100,000