Fair Value Measurement - Amount of Gains and Losses from Changes in Fair Value Included in Earnings (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value Inputs Assets Quantitative Information [Line Items]
Change in fair value			$ 2,900	$ 1,649
Construction [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Change in fair value	$ 2,149	$ 845	2,900	1,649
Total change in fair value	$ 2,149	$ 845	$ 2,900	$ 1,649