Income taxes: Income tax expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal		$ 135	$ (9)
State	$ (353)	(188)	4
Foreign	(209)	(202)	(96)
Deferred:
Federal	(24,150)	(8,175)	(5,867)
State	(430)	(1,047)	(1,959)
Foreign	(100)	146	111
Total income tax expense	$ (25,242)	$ (9,331)	$ (7,816)