Income Taxes - Reconciliation of beginning and ending amount of unrecognized tax benefits (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits [Roll Forward]
Balance at January 1	$ 2,215,000	$ 26,152,000
Additions based on tax positions related to the current year	0	0
Additions for tax positions of prior years	0	0
Reductions for tax positions of prior years	0	(23,937,000)
Balance at December 31	$ 2,215,000	$ 2,215,000