Joint Venture - Operating Results (Details) (Joint venture, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Joint venture
Schedule of Equity Method Investments [Line Items]
Revenues	$ 257,776	$ 269,657	$ 188,107
Net income	14,603	23,643	11,035
Current assets	92,421	111,263	71,611
Non-current assets	26,099	22,979	17,880
Current liabilities	14,315	59,952	32,828
Non-current liabilities	27,845	3,089	2,872
Members’ equity	76,360	71,199	53,791
Capital expenditures	5,259	6,736	2,271
Depreciation and amortization	$ 2,034	$ 1,603	$ 1,720