Equity - Additional Information (Detail) - USD ($)		3 Months Ended				9 Months Ended		12 Months Ended
	Mar. 28, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Issuance of common stock, net, shares	9,780,000	183,012
Proceeds from the issuance of common stock	$ 105,800,000	$ 2,900,000				$ 108,395,000	$ 163,466,000
Share price to the public (in usd per share)	$ 11.35
Dividends declared per common share (in usd per share)		$ 0.17	$ 0.17	$ 0.17	$ 0.16	$ 0.51	$ 0.48	$ 0.64
Dividend, payable date				Apr. 15, 2016
Dividend, record date				Mar. 31, 2016
Weighted Average [Member]
Class of Stock [Line Items]
Share price to the public (in usd per share)		$ 15.61				$ 15.61
Over-Allotment Option [Member]
Class of Stock [Line Items]
Issuance of common stock, net, shares	1,280,000
At-The-Market Offering [Member]
Class of Stock [Line Items]
Issuance of common stock, net, shares						183,012
Proceeds from the issuance of common stock						$ 2,900,000
Aggregate offering price of common stock			$ 125,000,000
Issuance costs reclassified to additional paid in capital						200,000
Remaining offering about available		$ 122,200,000				$ 122,200,000
At-The-Market Offering [Member] | Weighted Average [Member]
Class of Stock [Line Items]
Share price to the public (in usd per share)		$ 15.61				$ 15.61