Commitments and Contingencies (Details) (USD $)	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Commitments and Contingencies [Line Items]
Rent expense, operating leases	$ 4,200,000	$ 3,400,000
Self-insured health insurance, liability	334,000
Maximum [Member]
Commitments and Contingencies [Line Items]
Self-insured health insurance limit, per person	100,000
Self-insured health Insurance, aggregate liability based on participants and claims (percentage)	125.00%
Self-insured health insurance, estimated cumulative liability for annual contract	$ 3,000,000
Computer Equipment [Member] | Minimum [Member]
Commitments and Contingencies [Line Items]
Capital lease obligation, term	3 years
Computer Equipment [Member] | Maximum [Member]
Commitments and Contingencies [Line Items]
Capital lease obligation, term	5 years