Summary of Significant Accounting Policies (Details Textual) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011
Summary of Significant Accounting Policies (Textual) [Abstract]
Carrying value of credit agreement debt	$ 295,173,000		$ 295,173,000		$ 309,744,000
Summary of Significant Accounting Policies (Additional Textual) [Abstract]
Cost of postage	65,100,000	65,300,000	132,500,000	133,100,000
Restricted cash	2,900,000		2,900,000
Proceeds from the sale/maturity of short-term investments			16,800,000	17,700,000
Par Value of Convertible Debt	150,000,000		150,000,000
Estimated Fair Value of Convertible Debt	152,000,000		152,000,000
Short-term investment contractual maturities			1 year		1 year
Cash equivalents, maturity period			Three months or less
Credit agreement debt [Member]
Summary of Significant Accounting Policies (Textual) [Abstract]
Carrying value of credit agreement debt	173,000,000		173,000,000
Fair value of Credit Agreement debt	$ 184,000,000		$ 184,000,000