Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Treasury stock, shares	1,201,051	1,179,175
Class A
Common stock, par value	0.01	0.01
Common stock, shares authorized	80,000,000	80,000,000
Common stock, shares issued	56,778,718	42,916,668
Common stock, shares outstanding	55,577,667	41,737,493
Class B
Common stock, par value	0.01	0.01
Common stock, shares authorized	0	2,000,000
Common stock, shares issued	0	1,030,700
Common stock, shares outstanding	0	1,030,700