Income taxes: Effective Income Tax Rate Reconciliation (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) subsidiary	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Income taxes:
Number of Subsidiaries Filing Income Tax Returns | subsidiary	1
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Federal income tax (expense) benefit at statutory rates	$ (8,492)	$ (4,450)	$ (1,572)
State income tax, net of federal benefit	(1,080)	(1,710)	(590)
Impact of foreign operations	138	(179)	(267)
Non-deductible expenses	(590)	(1,253)	(659)
Change in tax reserves	175	128	165
Other	98	(16)	(191)
Change in valuation allowance-US	420	(336)	(580)
Total income before income taxes	$ (9,331)	$ (7,816)	$ (3,694)