Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 2,785	$ 3,260
Accumulated depreciation	285,271	245,629
Accumulated amortization	$ 25,215	$ 20,545
Common stock, $0.01 par value	$ 0.01	$ 0.01
Common stock shares authorized	100,000	100,000
Common stock shares issued	44,847	44,689
Treasury stock shares	930	862