CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 19,890	$ 19,083
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	394,955	364,124
Intangible assets, accumulated amortization	$ 129,881	$ 114,922
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	120,000,000	120,000,000
Common stock, issued	84,823,229	84,883,517
Common stock, outstanding	84,823,229	84,883,517