Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Accounts receivable, trade, allowance for doubtful accounts	$ 6,388	$ 6,064
Property and equipment, accumulated depreciation	$ 287,422	$ 272,148
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	62,696,162	62,408,868
Common stock, shares outstanding	55,750,947	57,079,039
Treasury stock, shares	6,945,215	5,329,829
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