Summary of Potential Number of Units that Could Vest Under Restricted Stock Unit Awards (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Restricted Stock Unit [Line Items]
Number of units at threshold IRR		84,554	47,640	65,832
Number of units at target IRR		169,107	95,282	131,683
Number of units at maximum IRR		253,661	142,917	197,515
Fair value of units at threshold IRR	[1]	$ 2,522	$ 2,057	$ 1,879
Fair value of units at target IRR	[1]	5,044	4,115	3,758
Fair value of units at maximum IRR	[1]	$ 7,568	$ 6,173	$ 5,637

[1] The grant date fair values for units issued during the years ended December 31, 2014, 2015, and 2016 were $28.54, $43.19 and $29.83, respectively.