Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Allowance for doubtful accounts	$ 1,532	$ 1,593
Common stock, par value	$ 1.50	$ 1.50
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	24,934,981	24,934,981
Treasury stock, shares	4,694,065	4,771,443