Summary of Significant Accounting Policies (Details 5) (USD $)	12 Months Ended
	Dec. 31, 2012	Mar. 31, 2013
Level 1 | Securities
Fair value measurement
Assets	$ 22,870,000	$ 22,773,000
Level 2 | Securities
Fair value measurement
Assets	788,000	775,000
Level 2 | Fuel hedge
Fair value measurement
Assets	631,000	808,000
Level 2 | Interest rate swap
Fair value measurement
Liabilities	4,586,000	4,178,000
Level 3 | Contingent consideration
Fair value measurement
Liabilities	4,401,000	9,401,000
Increase in a level 3 liability of the contingent consideration	5,000,000
Total | Securities
Fair value measurement
Assets	23,658,000	23,548,000
Total | Fuel hedge
Fair value measurement
Assets	631,000	808,000
Total | Contingent consideration
Fair value measurement
Liabilities	4,401,000	9,401,000
Total | Interest rate swap
Fair value measurement
Liabilities	$ 4,586,000	$ 4,178,000