Accounting for Stock Based Compensation - Summarizes Restricted Stock Unit Activity (Detail) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding at beginning of period, Shares	34,920	136,566	282,100
Granted, Shares	32,406	19,920	21,681
Vested, Shares	(32,420)	(91,566)	(130,684)
Forfeited, Shares		(30,000)	(36,531)
Outstanding at end of period, Shares	34,906	34,920	136,566
RSU
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding at beginning of period, Shares	331,821	215,969
Granted, Shares	288,798	220,146	215,969
Vested, Shares	(50,953)	(23,956)
Forfeited, Shares	(44,927)	(80,338)
Outstanding at end of period, Shares	524,739	331,821	215,969
RSU | Time Vesting Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding at beginning of period, Shares	141,741	86,392
Granted, Shares	132,864	107,391	86,392
Vested, Shares	(50,953)	(23,956)
Forfeited, Shares	(14,747)	(28,086)
Outstanding at end of period, Shares	208,905	141,741	86,392
RSU | ROIC Target Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding at beginning of period, Shares	95,041	64,785
Granted, Shares	77,967	56,380	64,785
Forfeited, Shares	(15,090)	(26,124)
Outstanding at end of period, Shares	157,918	95,041	64,785
RSU | TSR Target Shares [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding at beginning of period, Shares	95,039	64,792
Granted, Shares	77,967	56,375	64,792
Forfeited, Shares	(15,090)	(26,128)
Outstanding at end of period, Shares	157,916	95,039	64,792