Income Taxes - Federal and State tax credit carryforwards (Details) - USD ($)	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2015
Operating loss carryforwards
Excess tax benefits from exercise of employee stock option	$ 1,100,000
Valuation allowance on deferred tax assets	11,726,000	$ 10,561,000	$ 10,100,000
Deferred tax assets, tax credit carryforwards
Federal research credits	5,003,000	$ 3,557,000
Federal
Operating loss carryforwards
Operating loss carryforwards	5,600,000
Deferred tax assets, tax credit carryforwards
Federal alternative minimum tax credit carryforwards	1,100,000
Federal research credits	922,000
State
Operating loss carryforwards
Operating loss carryforwards	1,400,000
Deferred tax assets, tax credit carryforwards
Tax credit carryforwards	$ 555,000