Subsequent Events (Details Textual) (Subsequent Event [Member], Merger [Member], USD $)	6 Months Ended
	Jun. 30, 2012
Subsequent Event [Member] | Merger [Member]
Subsequent Event [Line Items]
Date of execution of merger agreement	Jul. 09, 2012
Merger agreement, offered price per share	$ 92.00
Merger agreement termination fee for reasons other than acceptance of a superior proposal	$ 146,000,000
Merger agreement termination fee related to acceptance of a superior proposal	73,000,000
Merger agreement, approximate purchase price, gross	$ 4,900,000,000
Expected period in which consummation of the merger will occur	first quarter of 2013