Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	300,000,000	300,000,000
Class A Common Stock
Common stock, shares issued	114,341,000	114,025,000
Common stock, shares outstanding	76,276,000	88,335,000
Common stock, shares held in treasury	38,065,000	25,690,000