Income taxes: Temporary differences comprising our net deferred tax assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014
Deferred Tax Assets:
Net operating loss carry-forwards		$ 370,344	$ 366,686
Depreciation and amortization			7,769
Tax credits		2,317	2,208
Equity-based compensation		1,474	849
Accrued liabilities and other			20,705
Total gross deferred tax assets		374,135	398,217
Deferred Tax Liabilities:
Depreciation and amortization		18,038
Accrued liabilities and other		97,417
Total gross deferred tax liabilities		115,455
Deferred tax assets (liabilities)
Net deferred tax assets before valuation allowance		258,680	398,217
Valuation allowance		(213,538)	(345,250)
Net deferred tax assets		$ 45,142	$ 52,967
Income tax benefit due to reduction in valuation allowance	$ 52,200