Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	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	475
Additions based on tax positions related to the current year
Additions for tax positions of prior year
Reductions for tax positions of prior years
Settlements
Balance at end of year	475	475
Interest accrued during the period related to unrecognized tax benefits	4	$ 5
Federal
Income taxes
Net operating loss carryforwards	11,300
Federal | General Business Tax Credit Carryforward
Income taxes
Tax credit carryforward	1,300
Federal | Alternative Minimum Tax Credit Carryforward
Income taxes
Tax credit carryforward	192
California
Income taxes
Net operating loss carryforwards	$ 28,600