Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010
Assets:
Cash	$ 47,502	$ 72,422
Cash equivalents	68,803	120,042
Short-term—marketable securities	46,006	31,192
Non-qualified Deferred Compensation Plan	3,635	2,971
Total	165,946	226,627
Liabilities:
Earnout Payment Liability	890	1,365
Non-qualified Deferred Compensation Plan	3,635	2,971
Total	4,525	4,336
Total Fair Value [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash	47,502	72,422
Cash equivalents	68,803	120,042
Short-term—marketable securities	46,006	31,192
Non-Qualified Deferred Compensation Plan	3,635	2,971
Total	165,946	226,627
Liabilities:
Earnout Payment Liability	890	1,365
Non-Qualified Deferred Compensation Plan	3,635	2,971
Total	4,525	4,336
Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash	0	0
Cash equivalents	40,793	120,042
Short-term—marketable securities	7,501	4,822
Non-Qualified Deferred Compensation Plan	3,635	2,971
Total	51,929	127,835
Liabilities:
Earnout Payment Liability	0	0
Non-Qualified Deferred Compensation Plan	3,635	2,971
Total	3,635	2,971
Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash	0	0
Cash equivalents	28,010	0
Short-term—marketable securities	38,505	26,370
Non-Qualified Deferred Compensation Plan	0	0
Total	66,515	26,370
Liabilities:
Earnout Payment Liability	0	0
Non-Qualified Deferred Compensation Plan	0	0
Total	0	0
Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Assets:
Cash
Cash equivalents	0	0
Short-term—marketable securities	0	0
Non-Qualified Deferred Compensation Plan	0	0
Total	0	0
Liabilities:
Earnout Payment Liability	890	1,365
Non-Qualified Deferred Compensation Plan	0	0
Total	890	1,365
Earnout Payment Liability [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Change in Estimate on Measurement With Unobservable Inputs	$ (681)	$ (467)