Segment information: (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 segment	Mar. 31, 2014	Dec. 31, 2014
Segment information
Number of operating segments	1
Revenues	$ 97,242	$ 92,937
Long lived assets, net	343,458		360,795
North America
Segment information
Revenues	79,638	73,043
Long lived assets, net	269,558		266,713
Europe
Segment information
Revenues	17,604	19,894
Long lived assets, net	$ 73,900		$ 94,082