Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions			3 Months Ended		6 Months Ended
	Aug. 08, 2017	Jul. 01, 2017	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2017	Jun. 30, 2016	Jul. 28, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Shares issued value					$ 211,977	$ 36,374
Proceeds from sale of available-for-sale securities					266
Note receivable due from related party			$ 251		$ 251			$ 251
At-the-Market Program [Member]
Subsequent Event [Line Items]
Number of shares issued			0.5	0.5	0.5
Shares issued value			$ 5,100		$ 5,100
Fees and commissions			$ 100		$ 100
Subsequent Event [Member]
Subsequent Event [Line Items]
Proceeds from sale of available-for-sale securities		$ 4,300
Note receivable due from related party							$ 251
Subsequent Event [Member] | At-the-Market Program [Member]
Subsequent Event [Line Items]
Number of shares issued	0.5
Shares issued value	$ 5,200
Fees and commissions	$ 200