Nature of operations and summary of significant accounting policies (Income Taxes) (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Federal corporate tax rate		21.00%
Deferred tax benefit	$ 0	$ 0
Uncertain tax positions	$ 0	0	$ 0
Estimated amount of cancellation of indebtedness income		$ 60,398,000
Net operating loss carryforwards			1,011,368,000
Net operating loss carryforwards subject to limitation			760,067,000
Net operating loss carryforwards not subject to limitation			251,301,000
Net operating loss carryforwards not subject to limitation expected in 2018			$ 85,863,000