Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (usd per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (shares)	5,000,000	5,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value (usd per share)	$ 5.00	$ 5.00
Common stock, shares authorized (shares)	150,000,000	150,000,000
Common stock, shares issued (shares)	49,990,248	49,990,248
Common stock, shares outstanding (shares)	49,392,978	49,321,231