Income Taxes - Reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 1987
Income taxes
Tax bad debt reserve			$ 3,000
Deferred tax liability not recorded on tax bad debt reserve balance	$ 1,000	$ 1,000
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Balance at beginning of year	$ 475	488
Additions based on tax positions related to the current year
Reductions for tax positions of prior years		(13)
Balance at end of year	$ 475	475
Unrecognized tax benefits if recognized would favorably affect income tax provision in future	475
Interest accrued during the period related to unrecognized tax benefits	5	$ 3
General Business Tax Credit Carryforward
Income taxes
Tax credit carryforward	1,100
Alternative Minimum Tax Credit Carryforward
Income taxes
Tax credit carryforward	172
Federal
Income taxes
Net operating loss carryforwards	11,900
California
Income taxes
Net operating loss carryforwards	$ 29,200