Preferred Stock - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended									12 Months Ended
	Sep. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, shares authorized (shares)										10,000,000
Preferred Stock, par value per share (usd per share)			$ 0.01							$ 0.01	$ 0.01
Distribution Amount Per Share (usd per share)	$ 0.421875	$ 0.421875	0.421875	$ 0.421875	$ 0.421875	$ 0.421875	$ 0.421875	$ 0.421875	$ 0.421875			$ 0.421875
Stock issuance costs										$ 1,947	$ 1,122	$ 491
6.75% Series C Cumulative Redeemable Perpetual Preferred Stock
Auction Market Preferred Securities, Stock Series [Line Items]
Preferred Stock, par value per share (usd per share)			$ 0.01							$ 0.01	$ 0.01
Dividend rate (percentage)										6.75%
Shares redeemed										$ 138,400
Stock issuance costs										$ 800