Stock-Based Compensation, Dividend Restrictions, and Calculations of Earnings Per Share of Common Stock - Schedule of Restricted Stock and Restricted Stock Units (Parenthetical) (Detail)	Dec. 31, 2014 shares
Executive Officer [Member] | Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested but not yet settled	36,110
Executive Officer [Member] | Time-Based Restricted Stock Units Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested but not yet settled	113,385
Executive Officer [Member] | Performance Based Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested but not yet settled	104,628
Director [Member] | Time-Based Restricted Stock Units Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares vested but not yet settled	30,784