Income Taxes - Effective income tax rate reconciliation, Amount (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Corporate tax rate (as a percent)	21.00%	34.00%
Reduction in deferred tax assets resulting from rate reduction		$ 2,572,000
Income tax expense benefit reconciliation
Federal income tax at statutory rate	$ (4,642,000)	(8,383,000)
State income tax, net of federal benefit	(1,300,000)	(1,096,000)
Effect of reduced corporate tax rates		2,644,000
Foreign tax differential	733,000	1,993,000
Permanent differences	178,000	2,549,000
Tax credits generated in current year	(783,000)	(362,000)
Other	1,000	269,000
Valuation allowance	$ 5,813,000	$ 2,386,000
Maximum
Income Taxes
Corporate tax rate (as a percent)		35.00%