Accrued and other liabilities: (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Accrued and other current liabilities
Operating accruals	$ 11,539	$ 8,283
Deferred revenue -current portion	4,174	4,132
Payroll and benefits	2,952	2,358
Taxes -non-income based	1,128	692
Interest	11,672	11,054
Total	31,465	26,519
Reconciliation of the amounts related to asset retirement obligations
Balance at the beginning of the period	256	239	233
Effect of exchange rates	11	5	(5)
Amortization of discount	12	12	11
Balance at the end of the period	$ 279	$ 256	$ 239