Summary of Significant Accounting Policies - Taxes and Retirement Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Taxes
Unrecognized tax benefit	$ 0	$ 0
Retirement Plan
Pension asset	332,000	179,000
Net (loss) gain recognized in other comprehensive income	$ 123,000	$ 513,000	$ 1,400,000