Other Comprehensive Loss (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Changes in components of accumulated other comprehensive loss
Balance	$ 34,633,000
Balance	36,317,000
Reclassifications out of accumulated other comprehensive income or loss, net of tax	0	$ 0
Tax effect	0	$ 0
Accumulated Other Comprehensive Income (Loss)
Changes in components of accumulated other comprehensive loss
Balance	(42,000)
Net unrealized loss on marketable securities	(4,000)
Balance	$ (46,000)