Stock Transactions and Unit Redemptions - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Jun. 22, 2016	Jun. 21, 2016	Oct. 27, 2015
Class of Stock [Line Items]
Payment percentage of the gross proceeds from the sale of shares	2.00%
Stock repurchase program and unit redemption remaining authorized amount	$ 279,350,247
Redemptions, Number of Units	2,927,758
Reduction cost due to redemption and repurchases of shares	$ 7,800,000
Reduction cost due to redemption and repurchases of shares per share	$ 11.07
Class A Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized	750,000,000		750,000,000	750,000,000	500,000,000
Common stock, issued during the period	9,942		2,004,533
Common stock outstanding	248,467,000		244,870,000
Maximum number of shares under the controlled equity offering	20,000,000
Common stock, shares issued	296,699,000		292,549,000
Company's repurchase and additional redemption authority amount						$ 300,000,000
Stock repurchase program and unit redemption remaining authorized amount	$ 279,400,000
Reduction in diluted shares due to redemption and repurchases of shares	700,000
Class A Common Stock [Member] | Controlled Equity Offerings [Member]
Class of Stock [Line Items]
Common stock, shares issued	16,819,294
Redemptions, Number of Units	2,800,000
Class B Common Stock [Member]
Class of Stock [Line Items]
Common stock, shares authorized	150,000,000		150,000,000	150,000,000	100,000,000
Common stock, issued during the period	0	0
Common stock outstanding	34,848,107	34,848,107	34,848,000
Common stock, shares issued	34,848,000		34,848,000