CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accounts receivable, allowance for doubtful accounts	$ 22,329	$ 19,083
Accumulated depreciation	426,019	364,124
Intangible assets, accumulated amortization	$ 151,025	$ 114,922
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	770,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	84,852,584	84,883,517
Common stock, outstanding	84,852,584	84,883,517
Series A Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	1,000,000	1,000,000
Preferred stock, shares issued	770,000
Preferred stock, shares outstanding	770,000