Stockholders' Equity - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Class of Stock [Line Items]
Underwritten public offering shares	8,400,000
Net proceeds from underwriting	$ 132,050,000
Conversion of Units to Common Stock	0	0
Compensation Expense Related to Restricted Shares Issued during the Quarter	1,008
Restricted Stock [Member]
Class of Stock [Line Items]
Restricted stock/unit awards to employees	284,461
Fair value of restricted stock/unit awards	4,719,000
Vesting period of restricted stock/unit awards to employees	3 years
Amortization Related to Restricted Stock and Unit Awards	1,826,000	1,099,000
Amount of Share Based Compensation Expense Capitalized	11,000	0
Unrecognized compensation expense related to restricted stock/unit awards	$ 6,310,000
Weighted average period during which unrecognized compensation expense is expected to be recognized	1 year 1 month 24 days
Series F Preferred Stock [Member]
Class of Stock [Line Items]
Minimum fixed coupon rate of preferred stock	2.375%
Number of years of U.S. treasury rate one	30 years
Number of years of U.S. treasury rate two	10 years
LIBOR rate	3 month LIBOR
New coupon rate of preferred stock	5.325%