CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Purchase price in excess of predecessor basis, tax benefit	$ 10,306
Treasury stock, shares	7,510,187	7,777,722
Class A Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	97,337,700	97,337,700
Common stock, shares issued	41,224,792	41,224,792
Common stock, shares outstanding	33,714,605	33,447,070
Class B Common Stock [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	662,300	662,300
Common stock, shares issued	662,296	662,296
Common stock, shares outstanding	662,296	662,296