Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
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	32,831,113	32,537,008
Common stock, shares outstanding	21,654,302	21,741,586
Class B [Member]
Common stock, par value	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	1,680,590	1,495,490
Common stock, shares outstanding	1,680,590	1,495,490