CONDENSED CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Short-term Investments	$ 15,048	$ 13,734
Common stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	280,000,000	280,000,000
Common stock, shares issued (in shares)	145,107,000	146,415,000
Common Stock, Shares, Outstanding	140,104,000	138,985,000
Treasury stock shares (in shares)	8,003,000	7,430,000
Tax effect of accumulated other comprehensive income	$ 0	$ 0