Commitments and Contingencies (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Complaint	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies [Line Items]
Number of derivative complaints	3
Rent expense, operating leases	$ 5,900,000	$ 4,600,000	$ 4,000,000
Operating Leases, Rent Expense, Sublease Rentals	5,000	0	145,000
Self-insured health insurance, liability	243,000	384,000
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	$ 3,000,000.0
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