13. Income taxes (Details) - Effective Tax Rate Reconciliation	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Effective Tax Rate Reconciliation [Abstract]
Federal statutory tax rate	34.00%	34.00%	34.00%
R&D credit	6.00%
State income taxes, net of federal income taxes	(0.50%)	0.10%	0.80%
Valuation allowance and tax accruals	(1.10%)	0.90%	0.90%
Uncertain tax positions	(1.00%)
Miscellaneous permanent items	(0.30%)	(8.30%)	(0.80%)
Other	0.10%	(2.30%)	0.30%
Effective tax rate	37.20%	24.40%	35.20%