CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Accounts receivable, allowance for doubtful accounts	$ 4,207	$ 4,096
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, authorized (in shares)	800,000	800,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized (in shares)	1,500,000,000	1,500,000,000
Common stock, issued (in shares)	147,718,000	147,047,000
Common stock, outstanding (in shares)	88,902,000	89,297,000
Treasury stock (in shares)	58,816,000	57,750,000
Common Class B
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, authorized (in shares)	39,000,000	39,000,000
Common stock, issued (in shares)	0	0
Common stock, outstanding (in shares)	0	0