Stockholders' Equity - Summary of Dividends/Distributions (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Class of Stock [Line Items]
Total Common Dividend/Distribution	$ 47,263		$ 38,862
Total Preferred Dividend/Distribution	1,019		8,733		18,947
Common Stock/Operating Partnership Units
Class of Stock [Line Items]
Total Common Dividend/Distribution	47,263		38,862		0
Series F Preferred Stock
Class of Stock [Line Items]
Total Preferred Dividend/Distribution	566	[1]	2,896		2,728
Series G Preferred Stock
Class of Stock [Line Items]
Total Preferred Dividend/Distribution	453	[1]	1,809		1,809
Series J Preferred Stock
Class of Stock [Line Items]
Total Preferred Dividend/Distribution			2,034	[1]	10,785	[1]
Series K Preferred Stock
Class of Stock [Line Items]
Total Preferred Dividend/Distribution			$ 1,994	[1]	$ 3,625

[1] See the "Preferred Stock" section for the redemptions and discussion of pro-rated dividends for all series of preferred stock occurring during the years ended December 31, 2014, 2013 and 2012.