Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Comprehensive Income (Loss)
Accumulated unrealized loss on available-for-sale securities at beginning of period			$ (17)	$ (134)
Change during the period	$ (1)	$ 13	$ 17	133
Accumulated unrealized loss on available-for-sale securities at end of period		$ (1)		$ (1)