Contingently Issuable Common Stock (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	0 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Dec. 10, 2010	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Business Combinations [Abstract]
Business acquisition, purchase price common shares		3.2
Business acquisition, common shares value		$ 19,400,000
Business acquisition, maximum shares issuable	4.2	10.2
Business acquisition, fair value of contingent payment	52,390,000	28,200,000	52,390,000		52,390,000
Business acquisition, closing stock price	$ 15.44		$ 15.44		$ 15.44
Business acquisition, contingent consideration, at fair value hypothetical value	64,400,000		64,400,000		64,400,000
Business acquisition, increase (decrease) common stock					$ 3.96
Business acquisition, percentage increase (decrease)					34.00%
Fair Value of Contingently Issuable Common Stock [Roll Forward]
December 31, 2011					38,700,000
Fair value adjustment of Contingent Payment during the period			1,240,000	8,600,000	13,690,000	8,600,000
June 30, 2012	$ 52,390,000	$ 28,200,000	$ 52,390,000		$ 52,390,000