Stockholders' Equity (Details)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reconciliation of the beginning and ending common stock outstanding
Balance, end of period	77,843,883	66,071,424	60,614,931
Common Stock [Member]
Reconciliation of the beginning and ending common stock outstanding
Balance, beginning of period	66,071,424	60,614,931	59,246,284
Issuance of common stock	11,681,392	5,287,098	1,244,914
Restricted stock-based awards, net of forfeitures	91,067	169,395	123,733
Balance, end of period	77,843,883	66,071,424	60,614,931