Stockholders Equity - Distributions Table (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Schedule of Stockholders' Equity [Line Items]
Paid in Cash	$ 49,363	$ 57,377
Reinvested in Shares	48,768	54,727
Total Distributions	98,131	112,104
September 30, 2014 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date	Oct. 15, 2014
Declared per Common Share	$ 0.15625
Paid in Cash	16,621
Reinvested in Shares	16,275
Total Distributions	32,896
June 30, 2014 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date	Jul. 15, 2014
Declared per Common Share	$ 0.15625
Paid in Cash	16,426
Reinvested in Shares	16,294
Total Distributions	32,720
March 31, 2014 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date	Apr. 15, 2014
Declared per Common Share	$ 0.15625
Paid in Cash	16,316
Reinvested in Shares	16,199
Total Distributions	32,515
December 31, 2013 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date		Jan. 15, 2014
Declared per Common Share		$ 0.15625
Paid in Cash		16,199
Reinvested in Shares		16,102
Total Distributions		32,301
September 30, 2013 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date		Oct. 15, 2013
Declared per Common Share		$ 0.15625
Paid in Cash		15,939
Reinvested in Shares		15,786
Total Distributions		31,725
June 30, 2013 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date		Jul. 15, 2013
Declared per Common Share		$ 0.15625
Paid in Cash		13,457
Reinvested in Shares		12,516
Total Distributions		25,973
March 31, 2013 [Member]
Schedule of Stockholders' Equity [Line Items]
Payment Date		Apr. 15, 2013
Declared per Common Share		$ 0.15625
Paid in Cash		11,782
Reinvested in Shares		10,323
Total Distributions		$ 22,105