Common Stock and Other Equity Related Transactions - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands							9 Months Ended
	Oct. 14, 2016	Sep. 30, 2016	Jul. 08, 2016	Jun. 30, 2016	Apr. 08, 2016	Mar. 31, 2016	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015	May 04, 2015
Class of Stock [Line Items]
Common stock, dividends paid (usd per share)			$ 0.4250		$ 0.425
Common Stock, par or stated value per share (usd per share)		$ 0.01					$ 0.01		$ 0.01
Commissions paid to sales agents							$ 824	$ 424
6.75% Series C Cumulative Redeemable Perpetual Preferred Stock
Class of Stock [Line Items]
Preferred stock dividends paid (usd per share)		$ 0.421875		$ 0.421875		$ 0.421875
Private Placement
Class of Stock [Line Items]
Aggregate Offering price										$ 125,000
Total gross proceeds							50,000
Common stock remained available for issuance		$ 75,000					$ 75,000
Private Placement | Common Stock
Class of Stock [Line Items]
Shares of common stock sold (shares)							683,548
Weighted average price per share (usd per share)							$ 73.15
Commissions paid to sales agents							$ 657
Subsequent Event [Member]
Class of Stock [Line Items]
Common stock, dividends paid (usd per share)	$ 0.4250