Annual report pursuant to Section 13 and 15(d)

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

v3.10.0.1
Summary of Potential Number of Units that Could Vest Under Restricted Stock Unit Awards (Detail) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure Of Restricted Stock Unit [Abstract]      
Number of units at threshold IRR 76,065 58,545 84,554
Number of units at target IRR 152,129 117,089 169,107
Number of units at maximum IRR 228,194 175,634 253,661
Fair value of units at threshold IRR [1] $ 2,967 $ 2,481 $ 2,522
Fair value of units at target IRR [1] 5,938 4,961 5,044
Fair value of units at maximum IRR [1] $ 8,906 $ 7,442 $ 7,568
[1] The grant date fair values for units issued during the years ended December 31, 2016 and 2017 were $29.83 and $42.37, respectively. The grant date fair values for the units issued during the year ended December 31, 2018 ranged from $37.55 to $39.03.