Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Accounts receivable, allowance	$ 7,270	$ 7,544
Accumulated amortization	$ 583,623	$ 527,153
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	475,000	475,000
Common stock, shares issued	85,459	84,272
Common stock, shares outstanding	83,367	84,180
Treasury stock, shares	2,092	92