Income Taxes - Additional Tax Disclosures (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 1987
Income taxes
Tax bad debt reserve			$ 3,000
Deferred tax liability not recorded on tax bad debt reserve balance	$ 632	$ 632
Tax bad debt deduction under the new method	$ 4,300
Taxable income evenly term	4 years
Unrecognized tax benefits if recognized would favorably affect income tax provision in future	$ 475	475
Interest accrued during the period related to unrecognized tax benefits	5	$ 5
Federal
Income taxes
Net operating loss carryforwards	8,200
Federal | General Business Tax Credit Carryforward
Income taxes
Tax credit carryforward	1,500
Federal | Alternative Minimum Tax Credit Carryforward
Income taxes
Tax credit carryforward	119
California
Income taxes
Net operating loss carryforwards	$ 25,300