Stock-Based Compensation, Dividend Restrictions, and Calculations of Earnings Per Share of Common Stock - Weighted Average Grant Date Fair Value Per Share (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value per share of award granted during the year		$ 26.80
Performance-Based Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value per share of award granted during the year	$ 26.10	27.01
Time-Based Restricted Stock Units Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value per share of award granted during the year	27.40	19.77	$ 19.70
Performance Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant-date fair value per share of award granted during the year	$ 26.08	$ 18.53	$ 17.03