Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accumulated depreciation, buildings	$ 317,777	$ 292,049
Accumulated depreciation, machinery and equipment	$ 726,576	$ 668,950
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	450,000,000	450,000,000
Common stock, shares issued (in shares)	146,652,615	148,410,422
Common stock, shares outstanding (in shares)	146,652,615	148,410,422