Convertible Debt (Details) (USD $)	9 Months Ended							1 Months Ended	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011		Sep. 30, 2012 Convertible Senior Notes [Member]	Dec. 31, 2011 Convertible Senior Notes [Member]	Feb. 29, 2008 Convertible Senior Notes [Member]	Feb. 29, 2008 Convertible Senior Notes [Member] 2013 Convertible Senior Notes [Member]	Sep. 30, 2012 Convertible Senior Notes [Member] 2013 Convertible Senior Notes [Member]	Sep. 30, 2011 Convertible Senior Notes [Member] 2013 Convertible Senior Notes [Member]	Sep. 30, 2012 Convertible Senior Notes [Member] 2013 Convertible Senior Notes [Member]	Sep. 30, 2011 Convertible Senior Notes [Member] 2013 Convertible Senior Notes [Member]	Jun. 29, 2012 Convertible Senior Notes [Member] 2015 Convertible Senior Notes [Member]	Sep. 30, 2012 Convertible Senior Notes [Member] 2015 Convertible Senior Notes [Member]	Sep. 30, 2012 Convertible Senior Notes [Member] 2015 Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount								$ 55,000,000
Debt Instrument, Interest Rate, Stated Percentage								2.75%					4.50%
Proceeds from (Repayments of) Short-term Debt	(10,081,000)	0
Debt Instrument, Convertible, Conversion Ratio								76.7448					117.2333
Debt Instrument, Convertible, Conversion Ratio, Principal Amount								0					1,000
Debt Instrument, Convertible, Conversion Price							$ 13.03	$ 13.03					$ 8.53
Debt Instrument, Convertible, Difference Between Capped Call Price Per Share and Conversion Price Per Share								$ 10.055
Debt Instrument, Convertible, Conversion Price, Capped Call Price Per Share								$ 23.085
Debt Instrument, Convertible, Capped Call Transaction, Shares Delivered on Settlement Date								91,904
Debt Instrument, Convertible, Capped Call Transaction, Settlement Tranche								211,000
Debt Instrument, Capped Call Transaction, Settlement Period								20 days
Debt Instrument, Convertible, Shares Covered by Capped Call Transaction								4,200,000
Debt Instrument, Call Feature, Call Price, Percent of Principal								100.00%					100.00%
Effective interest rate									3.73%	3.64%	3.73%	3.64%		4500.00%	4.50%
Contractually stated interest costs									351,000	344,000	970,000	1,032,000
Amortization of interest costs									131,000	112,000	352,000	336,000
Convertible Senior Notes, Total	34,900,000
Convertible senior notes	18,000,000		45,000,000	[1]
Convertible senior notes, current	16,919,000		0
Debt Instrument, Fair Value Disclosure					$ 35,000,000	$ 41,800,000

[1] (A)As adjusted to reflect the impact of additional tax-related adjustments to the Company's purchase accounting for Continuous Computing in accordance with ASC 805-10 "Business Combinations." See Note 2 — Acquisitions for additional information.