Details of Selected Balance Sheet Accounts - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary of intangible assets, net
Gross Amount	$ 34,400	$ 36,934
Accumulated Amortization	(32,734)	(33,831)
Net	1,666	3,103
Amortization expenses	1,400	1,700	$ 1,900
Customer relationships
Summary of intangible assets, net
Gross Amount	34,400	36,934
Accumulated Amortization	(32,734)	(33,831)
Net	$ 1,666	$ 3,103