Restricted Stock, Performance Share and Cash Awards - Schedule of Restricted Stock Awards Vesting Periods (Detail) - Restricted Stock Units Granted [Member] - shares	3 Months Ended			12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Vesting Period [Line Items]
Shares granted in the period	405,870	399,900	420,200	422,610	414,700	439,100
Vesting Period One Year [Member]
Vesting Period [Line Items]
Shares granted in the period				16,740	14,800	18,900
Vesting period, years				1 year
Vesting Period Two Years [Member]
Vesting Period [Line Items]
Shares granted in the period				8,870	12,000	12,700
Vesting period, years				2 years
Vesting Period Five Years [Member]
Vesting Period [Line Items]
Shares granted in the period				397,000	387,900	407,500
Vesting period, years				5 years