Restricted Stock, Performance Share and Cash Awards - Schedule of Restricted Stock Awards Vesting Periods (Detail) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Vesting Period [Line Items]
Shares granted in the period	414,700	439,100	476,350
Vesting Period One Year [Member]
Vesting Period [Line Items]
Shares granted in the period	14,800	18,900	21,600
Vesting period, years	1 year
Vesting Period Two Years [Member]
Vesting Period [Line Items]
Shares granted in the period	12,000	12,700	12,750
Vesting period, years	2 years
Vesting Period Five Years [Member]
Vesting Period [Line Items]
Shares granted in the period	387,900	407,500	442,000
Vesting period, years	5 years