Consolidated Balance Sheets [Parenthetical] - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Balance Sheets Parenthetical [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 4,880	$ 3,534
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	64,495,000	64,075,000
Common stock, shares outstanding	51,807,000	54,055,000
Treasury stock at cost, shares	12,688,000	10,200,000