Summary of Significant Accounting Policies - Components of other operating income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Other Operating Income [Abstract]
Property lease guaranty revenue	$ 3,058	$ 3,890	$ 4,430
Interest income	473	579	731
Management fee income	369	370	289
Other	249	208	215
Other operating	$ 4,149	$ 5,047	$ 5,665