Summary of Significant Accounting Policies (Cash Equivalents, Short-term Investments, and Stock-Based Compensation) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash equivalent, maturitypPeriod	3 months
Excess tax benefit from share-based compensation	$ 982	$ 905
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Short-term investments, maturity period	3 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Short-term investments, maturity period	1 year