Summary of Significant Accounting Policies Earnings per share (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Summary of Significant Accounting Policies [Abstract]
Weighted Average Number of Shares Outstanding, Basic	41,418,470	41,292,819	40,994,082	35,182,811	33,879,777	32,794,553	31,664,869	30,847,403	39,743,433	32,306,322	29,914,801
Incremental Common Shares Attributable to Share-based Payment Arrangements									1,514,864	2,775,289	0
Weighted Average Number of Shares Outstanding, Diluted	41,418,470	42,857,880	42,453,782	36,448,005	33,879,777	35,105,354	31,664,869	33,411,093	41,258,297	35,081,611	29,914,801
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									77,760	14,768	5,144,960