Significant Accounting Policies (Details Textual) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Entity	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Effective Income Tax Rate Reconciliation, Percent	(113.70%)	31.30%	41.00%
Decrease in Income Tax Expenses Unrecognized Tax Benefits if Recognized Net of Federal Tax	$ 315.9
Wholly-owned bankruptcy remote special-purpose corporations | Entity	1
Interest expense net of interest income on bank deposits	$ 3.1	$ 1.9	$ 1.1