Stockholders' Equity - Summary of Authorized Outstanding Preferred and Common Stock (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Common stock, shares authorized	40,000,000	40,000,000
Common stock, shares outstanding	31,894,563	31,621,870	31,194,892
Common stock, par value	$ 1.00	$ 1.00
Common stock dividend payment terms	As declared
Common stock, voting rights	Voting
Senior Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0
Preferred stock, par value	$ 1.00	$ 1.00
Preferred stock, dividend payment terms	As declared
Preferred stock, voting rights	Voting
Cumulative Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized	900,000	900,000
Preferred stock, shares outstanding	0
Preferred stock, par value	$ 5.00	$ 5.00
Preferred stock, dividend payment terms	As declared
Preferred stock, voting rights	Non-voting