Acquisitions (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Business Acquisition [Line Items]
Goodwill	$ 55,419,000	$ 9,900,000
Federal statutory tax rate, percent	35.00%	35.00%	35.00%
Effective tax rate, percent	26.10%	26.10%	41.30%
Kenny [Member]
Business Acquisition [Line Items]
Total purchase price	141,546,000
Post-closing adjustments expected to be paid	8,700,000
Number of employees	475
Number of offices in network	12
Goodwill	45,519,000
Trade receivables included in fair value of assets acquired	61,600,000
Retention receivables included in fair value of assets acquired	27,100,000
Gross amout due under contracts	88,725,000
Federal statutory tax rate, percent	39.00%
Effective tax rate, percent	36.00%
Acquisition-related costs	4,400,000
Notes Payable to Banks [Member]
Business Acquisition [Line Items]
Proceeds from borrowing under existing credit facility	$ 70,000,000