Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Accounts receivable, trade, allowance for doubtful accounts	$ 4,059	$ 4,276
Property and equipment, accumulated depreciation	$ 194,873	$ 186,242
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	45,000,000	45,000,000
Preferred stock, shares issued	0	0
Treasury stock, shares	1,210,271	1,210,271
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	62,007,567	61,762,944
Common stock, shares outstanding	60,797,296	60,552,673
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