Income Taxes - Unrecognized tax benefits (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Additions based on tax positions related to the current year	$ 3,405,000
Balance at end of period	3,405,000
Uncertain tax liabilities that, if recognized, would affect the annual effective tax rate	$ 0