Annual report pursuant to Section 13 and 15(d)

Summary of Potential Number of Units that Could Vest Under Restricted Stock Unit Awards (Detail)

v3.20.4
Summary of Potential Number of Units that Could Vest Under Restricted Stock Unit Awards (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Disclosure Of Restricted Stock Unit [Abstract]      
Number of units at threshold IRR 190,707 136,285 76,065
Number of units at target IRR 286,060 204,427 152,129
Number of units at maximum IRR 436,681 306,651 228,194
Fair value of units at threshold IRR [1] $ 6,125 $ 5,011 $ 2,967
Fair value of units at target IRR [1] 9,188 7,517 5,938
Fair value of units at maximum IRR [1] $ 14,026 $ 11,276 $ 8,906
[1] The grant date fair value for units issued during the year ended December 31, 2018 ranged from $37.55 to $39.03. The grant date fair value for the units issued during the year ended December 31, 2019 was $36.77 per share  .The grand date fair value for the units issued during the year ended  December 31, 2020