Condensed Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 3,712	$ 3,534
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	64,103,000	64,075,000
Common stock, shares outstanding (in shares)	53,151,000	54,055,000
Treasury stock at cost (in shares)	10,952,000	10,020,000