Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2017	Dec. 31, 2016
Stockholders' Equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,250,000,000	750,000,000
Common stock, shares issued (in shares)	547,421,654	542,317,788
Common stock, shares outstanding (in shares)	421,525,799	418,941,713
Treasury stock, shares (in shares)	125,895,855	123,376,075