Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013
Common stock, par value	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000	150,000,000	150,000,000	150,000,000
Common stock, shares issued	79,263,000	78,102,000	78,049,000	77,877,000	77,048,000
Treasury stock, shares	31,310,000	30,619,000	29,906,000	29,093,000	25,920,000