Debt (Details Textual) (USD $)	1 Months Ended	3 Months Ended	9 Months Ended
	Jan. 31, 2012	Sep. 30, 2012	Sep. 30, 2012	Jul. 01, 2012	Dec. 31, 2011
Debt (Additional Textual) [Abstract]
Revolving credit agreement, weighted-average interest rate		1.80%	1.80%		1.90%
Increase in revolving credit facility	$ 200,000,000
Revolving credit facility expand	300,000,000
Reduced the applicable margin by basis points Percentage	2.50%
Revolving credit agreement current		102,900,000	102,900,000		72,800,000
Revolving credit agreement		94,500,000	94,500,000		74,400,000
Maximum revolving credit agreement		200,000,000	200,000,000		150,000,000
Percentage of commitment fee			0.30%
Amount of swap agreement				50,000,000
Interest rate swap agreements of long-term debt		25,000,000	25,000,000
Unrealized loss on cash flow hedges		715,000	1,547,000
Accrued liability		198,000	198,000
Non-current liability		1,349,000	1,349,000
Letter of credit [Member]
Debt (Textual) [Abstract]
Standby letters of credit		$ 2,600,000	$ 2,600,000		$ 2,800,000