Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	12,000	12,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	32,241,699	31,951,945
Common stock, shares outstanding	21,877,529	21,587,775
Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	1,495,490	1,495,490
Common stock, shares outstanding	1,495,490	1,495,490