Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 15, 2015	Mar. 31, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Class of Stock
Common stock shares issued			123,140,501		123,140,501		123,110,454
Proceeds from issuance of common stock					$ 122	$ 135
Common stock dividend declared, per share			$ 0.45	$ 0.5	$ 0.90	$ 1.00
Incentive Plan | Restricted Stock Units (RSUs)
Class of Stock
Number of restricted stock units vested		17,783
Incentive Plan | Employee | Restricted Stock Units (RSUs)
Class of Stock
Restricted stock issued					17,652
Common Stock
Class of Stock
Stock repurchase program, remaining number of shares authorized to be repurchased			14,841,784		14,841,784
Common stock dividend declared, per share	$ 0.45
Dividend payable date					Jul. 28, 2015
Dividend payable, date of record					Jun. 26, 2015
Common Stock | DRSPP
Class of Stock
Common stock shares issued			7,756		7,756
Price of per share of stock issued			$ 15.75		$ 15.75
Proceeds from issuance of common stock					$ 122
Common Stock | Incentive Plan
Class of Stock
Common stock options reserved for issuance			1,000,000		1,000,000
Incentive plan termination year					2019
Compensation expense recognized			$ 85	$ 60	$ 170	$ 112
Restricted stock issued			5,412.000	3,079	10,744	5,824
Common stock shares issued in exchange for restricted stock		11,547
Common Stock | Incentive Plan | Employee
Class of Stock
Compensation expense recognized			$ 67	$ 80	$ 137	$ 161
Preferred Stock
Class of Stock
Preferred Stock, redemption price per share			$ 25		$ 25
Series A Cumulative Redeemable Preferred Stock
Class of Stock
Preferred stock dividend rate					7.75%
Preferred Stock, liquidation preference (dollars per share)			25		$ 25
Preferred Stock, dividends per annum (dollars per share)					$ 1.9375
Dividend payable date					Jul. 27, 2015
Dividend payable, date of record					Jul. 01, 2015
Series A preferred stock dividend, per share	0.4844
Series B Cumulative Redeemable Preferred Stock
Class of Stock
Preferred stock dividend rate					7.75%
Preferred Stock, liquidation preference (dollars per share)			$ 25		$ 25
Preferred Stock, dividends per annum (dollars per share)					$ 1.9375
Dividend payable date					Sep. 28, 2015
Dividend payable, date of record					Sep. 05, 2015
Series A preferred stock dividend, per share	$ 0.4844
Three-month LIBOR rate | Series B Cumulative Redeemable Preferred Stock
Class of Stock
Preferred stock dividend variable rate spread			5.18%		5.18%