Capital Stock	12 Months Ended
Dec. 31, 2018
Equity [Abstract]
Capital Stock	Capital Stock Common Stock Issuance On February 22, 2016, the Company entered into an underwriting agreement, pursuant to which the Company sold an aggregate of 44.0 million shares of common stock at a price to the Company of $19.675 per share. On February 26, 2016, the Company received $865.7 million in net proceeds, after deducting underwriting discounts and commissions. On March 2, 2016, the Company sold an additional 6.6 million shares of common stock as a result of the exercise of the underwriters’ option to purchase additional shares and received $129.9 million in net proceeds. These net proceeds were used for general corporate purposes, including repaying indebtedness under the Company’s revolving credit facility and repurchasing certain of the Company's senior notes. Incentive Plans On May 1, 2014, the Company’s shareholders approved the 2014 Incentive Plan. Under the 2014 Incentive Plan, incentive and non-statutory stock options, stock appreciation rights (SARs), stock awards, cash awards and performance share awards may be granted to key employees, consultants and officers of the Company. Non-employee directors of the Company may be granted discretionary awards under the 2014 Incentive Plan consisting of stock options or stock awards. A total of 18.0 million shares of common stock may be issued under the 2014 Incentive Plan. Under the 2014 Incentive Plan, no more than 10.0 million shares may be issued pursuant to incentive stock options. No additional awards may be granted under the 2014 Incentive Plan on or after May 1, 2024. At December 31, 2018, approximately 13.7 million shares are available for issuance under the 2014 Incentive Plan. No additional awards will be granted under any of the Company’s prior plans, including the 2004 Incentive Plan. Awards outstanding under the 2004 Incentive Plan will remain outstanding in accordance with their original terms and conditions. Treasury Stock In August 1998, the Board of Directors authorized a share repurchase program under which the Company may purchase shares of common stock in the open market or in negotiated transactions. The timing and amount of these stock purchases are determined at the discretion of management. The Company may use the repurchased shares to fund stock compensation programs presently in existence, or for other corporate purposes. All purchases executed to date have been through open market transactions. There is no expiration date associated with the authorization to repurchase shares of the Company. During the years ended December 31, 2018 and 2017, the Company repurchased 38.5 million shares for a total cost of $904.1 million and 5.0 million shares for a total cost of $123.7 million, respectively. During 2016, there were no share repurchases. Since the authorization date and subsequent authorizations, the Company has repurchased 73.4 million shares, of which 20.0 million shares have been retired, for a total cost of approximately $1.4 billion. No treasury shares have been delivered or sold by the Company subsequent to the repurchase. In February 2018, the Board of Directors authorized an increase of 25.0 million shares to the Company’s share repurchase program. In July 2018, the Board of Directors authorized an additional increase of 20.0 million shares to the Company’s share repurchase program. As of December 31, 2018, 53.4 million shares were held as treasury stock, which includes 1.4 million shares that were repurchased prior to December 31, 2018 and settled in January 2019. As of December 31, 2018, 11.6 million shares were available for repurchase under the repurchase plan. Dividend Restrictions The Board of Directors of the Company determines the amount of future cash dividends, if any, to be declared and paid on the common stock depending on, among other things, the Company's financial condition, funds from operations, the level of its capital and exploration expenditures, and its future business prospects. None of the senior note or credit agreements in place have restricted payment provisions or other provisions limiting dividends. In January 2018, the Board of Directors approved an increase in the quarterly dividend on the Company's common stock from $0.05 per share to $0.06 per share. In October 2018, the Board of Directors approved an additional increase in the quarterly dividend on the Company's common stock from $0.06 per share to $0.07 per share.

Capital Stock

Common Stock Issuance

On February 22, 2016, the Company entered into an underwriting agreement, pursuant to which the Company sold an aggregate of 44.0 million shares of common stock at a price to the Company of $19.675 per share. On February 26, 2016, the Company received $865.7 million in net proceeds, after deducting underwriting discounts and commissions. On March 2, 2016, the Company sold an additional 6.6 million shares of common stock as a result of the exercise of the underwriters’ option to purchase additional shares and received $129.9 million in net proceeds. These net proceeds were used for general corporate purposes, including repaying indebtedness under the Company’s revolving credit facility and repurchasing certain of the Company's senior notes.

Incentive Plans

On May 1, 2014, the Company’s shareholders approved the 2014 Incentive Plan. Under the 2014 Incentive Plan, incentive and non-statutory stock options, stock appreciation rights (SARs), stock awards, cash awards and performance share awards may be granted to key employees, consultants and officers of the Company. Non-employee directors of the Company may be granted discretionary awards under the 2014 Incentive Plan consisting of stock options or stock awards. A total of 18.0 million shares of common stock may be issued under the 2014 Incentive Plan. Under the 2014 Incentive Plan, no more than 10.0 million shares may be issued pursuant to incentive stock options. No additional awards may be granted under the 2014 Incentive Plan on or after May 1, 2024. At December 31, 2018, approximately 13.7 million shares are available for issuance under the 2014 Incentive Plan.

No additional awards will be granted under any of the Company’s prior plans, including the 2004 Incentive Plan. Awards outstanding under the 2004 Incentive Plan will remain outstanding in accordance with their original terms and conditions.

Treasury Stock

In August 1998, the Board of Directors authorized a share repurchase program under which the Company may purchase shares of common stock in the open market or in negotiated transactions. The timing and amount of these stock purchases are determined at the discretion of management. The Company may use the repurchased shares to fund stock compensation programs presently in existence, or for other corporate purposes. All purchases executed to date have been through open market transactions. There is no expiration date associated with the authorization to repurchase shares of the Company.

During the years ended December 31, 2018 and 2017, the Company repurchased 38.5 million shares for a total cost of $904.1 million and 5.0 million shares for a total cost of $123.7 million, respectively. During 2016, there were no share repurchases. Since the authorization date and subsequent authorizations, the Company has repurchased 73.4 million shares, of which 20.0 million shares have been retired, for a total cost of approximately $1.4 billion. No treasury shares have been delivered or sold by the Company subsequent to the repurchase.

In February 2018, the Board of Directors authorized an increase of 25.0 million shares to the Company’s share repurchase program. In July 2018, the Board of Directors authorized an additional increase of 20.0 million shares to the Company’s share repurchase program. As of December 31, 2018, 53.4 million shares were held as treasury stock, which includes 1.4 million shares that were repurchased prior to December 31, 2018 and settled in January 2019. As of December 31, 2018, 11.6 million shares were available for repurchase under the repurchase plan.

Dividend Restrictions

The Board of Directors of the Company determines the amount of future cash dividends, if any, to be declared and paid on the common stock depending on, among other things, the Company's financial condition, funds from operations, the level of its capital and exploration expenditures, and its future business prospects. None of the senior note or credit agreements in place have restricted payment provisions or other provisions limiting dividends.

In January 2018, the Board of Directors approved an increase in the quarterly dividend on the Company's common stock from $0.05 per share to $0.06 per share. In October 2018, the Board of Directors approved an additional increase in the quarterly dividend on the Company's common stock from $0.06 per share to $0.07 per share.