Summary of Significant Accounting Policies - Interest Cost Capitalized and Incurred (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Interest incurred									$ 2,538	$ 1,962	$ 2,180
Interest capitalized									1,210	714	379
Interest expense	$ 497	$ 344	$ 158	$ 329	$ 414	$ 313	$ 146	$ 375	$ 1,328	$ 1,248	$ 1,801