CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Accounts receivable, allowance for doubtful accounts	$ 22,964	$ 22,329
Property, plant and equipment, accumulated depreciation	453,753	426,019
Intangible assets, accumulated amortization	$ 170,507	$ 151,025
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized (in shares)	120,000,000	120,000,000
Common stock, issued (in shares)	84,829,822	84,852,584
Common stock, outstanding (in shares)	84,829,822	84,852,584
Series A preferred stock
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized (in shares)	1,000,000	1,000,000
Preferred stock, issued (in shares)	770,000	770,000
Preferred stock, outstanding (in shares)	770,000	770,000