Stockholders' Equity - Additional Information (Detail) - At the Market Equity Distribution Agreement [Member]		1 Months Ended	3 Months Ended	6 Months Ended
	May 06, 2016 USD ($) sales_agent	Aug. 09, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) shares	Jun. 30, 2018 USD ($) shares
Changes In Equity And Comprehensive Income Line Items [Line Items]
Aggregate offering price of common share	$ 400,000,000
Number of sales agents | sales_agent	5
Shares, issued | shares			0	0
Value of stock available for issuance under ATM			$ 349,375,000	$ 349,375,000
Subsequent Event [Member]
Changes In Equity And Comprehensive Income Line Items [Line Items]
Shares, issued | shares		343,251
Average price per share | $ / shares		$ 99.75
Net proceeds		$ 33,897,000