Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	300,000	300,000
Class A Common Stock
Common stock, shares issued	112,339	111,725
Common stock, shares outstanding	95,678	99,244
Common stock, shares held in treasury	16,661	12,481