Financing Activity - Applicable Credit Spread Over Libor at Various Leverage Levels (Detail) (2013 Revolving Credit Facility [Member])	6 Months Ended
	Jun. 30, 2013
Credit Spread Option [Member] | Level 1[Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Applicable Margin	1.50%
Credit Spread Option [Member] | Level 2 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Applicable Margin	1.70%
Credit Spread Option [Member] | Level 3 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Applicable Margin	1.85%
Credit Spread Option [Member] | Level 4 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Applicable Margin	2.05%
Minimum [Member] | Level 2 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Ratio of Total Liabilities to Gross Asset Value	0.450
Minimum [Member] | Level 3 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Ratio of Total Liabilities to Gross Asset Value	0.500
Minimum [Member] | Level 4 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Ratio of Total Liabilities to Gross Asset Value	0.550
Maximum [Member] | Level 1[Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Ratio of Total Liabilities to Gross Asset Value	0.450
Maximum [Member] | Level 2 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Ratio of Total Liabilities to Gross Asset Value	0.500
Maximum [Member] | Level 3 [Member]
Schedule Of Maximum Leverage Ratio [Line Items]
Ratio of Total Liabilities to Gross Asset Value	0.550