Capital Stock	12 Months Ended
Dec. 31, 2011
Capital Stock [Abstract]
Capital Stock	8. Capital Stock The total number of shares of capital stock which the Company has the authority to issue is 100,000,000 shares of common stock with a par value of $0.001 per share and 10,000,000 shares of preferred stock with a par value of $0.001 per share. The Board of Directors has the authority to increase the authorized amounts, or to classify any unissued shares by setting or changing in any one or more respects the preferences, conversion or other rights, voting powers, restrictions, limitations as to dividends, qualifications or terms or conditions of redemption of such shares. *Issuance of Common Stock* On January 5, 2011, the Company completed a secondary public offering of 11,500,000 shares of its common stock, including 1,500,000 shares pursuant to the underwriters' overallotment option, at a price to the public of $28.75 per share, and received net proceeds of approximately $325,707 after the payment of underwriting discounts and expenses. On March 18, 2011, the Company completed a secondary public offering of 14,500,000 shares of its common stock at a price to the public of $28.50 per share, and received net proceeds of approximately $407,606 after the payment of underwriting discounts and expenses. On April 1, 2011, the Company issued 2,175,000 shares pursuant to the underwriters' overallotment option from its March 18, 2011 secondary offering at a price to the public of $28.50 per share and received gross proceeds of approximately $61,985 before the payment of underwriting discounts and expenses. *Issuance of Common Stock – CEO Program* On October 9, 2009, the Company entered into a Sales Agreement (the "Sales Agreement") with Cantor Fitzgerald & Co. ("Cantor") to create a controlled equity offering program (the "CEO Program"). Under the terms of the Sales Agreement, the Company may offer and sell up to 5,000,000 shares of its common stock from time to time through Cantor, acting as agent and/or principal. Sales of the shares of common stock, if any, may be made in private transactions, negotiated transactions or any method permitted by law deemed to be an "at the market" offering as defined in Rule 415 under the Securities Act of 1933, as amended, including sales made directly on the New York Stock Exchange or to or through a market maker other than on an exchange. For the year ended December 31, 2011 and 2010, the Company issued 2,361,500 and 2,314,600 shares of common stock in at-the-market transactions, raising net proceeds to the Company, after sales commissions and fees of $66,221 and $65,731, respectively. The total commission and fees charged to additional paid in capital in connection with the issuance of these shares in 2011 and 2010 was $1,037 and $1,530, respectively. The shares of common stock issuable pursuant to the CEO Program are registered with the SEC on the Company's Registration Statement on Form S-3 (No. 333-159145), which became effective upon filing on October 9, 2009.

Capital Stock

12 Months Ended

Dec. 31, 2011

8. Capital Stock

The total number of shares of capital stock which the Company has the authority to issue is 100,000,000 shares of common stock with a par value of $0.001 per share and 10,000,000 shares of preferred stock with a par value of $0.001 per share. The Board of Directors has the authority to increase the authorized amounts, or to classify any unissued shares by setting or changing in any one or more respects the preferences, conversion or other rights, voting powers, restrictions, limitations as to dividends, qualifications or terms or conditions of redemption of such shares.

Issuance of Common Stock

On January 5, 2011, the Company completed a secondary public offering of 11,500,000 shares of its common stock, including 1,500,000 shares pursuant to the underwriters' overallotment option, at a price to the public of $28.75 per share, and received net proceeds of approximately $325,707 after the payment of underwriting discounts and expenses.

On March 18, 2011, the Company completed a secondary public offering of 14,500,000 shares of its common stock at a price to the public of $28.50 per share, and received net proceeds of approximately $407,606 after the payment of underwriting discounts and expenses.

On April 1, 2011, the Company issued 2,175,000 shares pursuant to the underwriters' overallotment option from its March 18, 2011 secondary offering at a price to the public of $28.50 per share and received gross proceeds of approximately $61,985 before the payment of underwriting discounts and expenses.

Issuance of Common Stock – CEO Program

On October 9, 2009, the Company entered into a Sales Agreement (the "Sales Agreement") with Cantor Fitzgerald & Co. ("Cantor") to create a controlled equity offering program (the "CEO Program"). Under the terms of the Sales Agreement, the Company may offer and sell up to 5,000,000 shares of its common stock from time to time through Cantor, acting as agent and/or principal. Sales of the shares of common stock, if any, may be made in private transactions, negotiated transactions or any method permitted by law deemed to be an "at the market" offering as defined in Rule 415 under the Securities Act of 1933, as amended, including sales made directly on the New York Stock Exchange or to or through a market maker other than on an exchange. For the year ended December 31, 2011 and 2010, the Company issued 2,361,500 and 2,314,600 shares of common stock in at-the-market transactions, raising net proceeds to the Company, after sales commissions and fees of $66,221 and $65,731, respectively. The total commission and fees charged to additional paid in capital in connection with the issuance of these shares in 2011 and 2010 was $1,037 and $1,530, respectively. The shares of common stock issuable pursuant to the CEO Program are registered with the SEC on the Company's Registration Statement on Form S-3 (No. 333-159145), which became effective upon filing on October 9, 2009.