Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts receivable, trade, allowance for doubtful accounts	$ 5,502	$ 4,307
Property and equipment, accumulated depreciation	$ 231,313	$ 209,236
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	45,000,000	45,000,000
Preferred stock, shares issued	0	0
Common Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	360,000,000	360,000,000
Common stock shares issued	62,407,876	62,120,102
Common stock, shares outstanding	60,386,220	60,909,831
Treasury stock, shares	2,021,656	1,210,271
Common Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common stock shares issued	11,484,408	11,484,408
Common stock, shares outstanding	11,484,408	11,484,408