Debt - Revolving Credit Facility - Additional Information (Detail) (Unsecured Revolving Credit Facility [Member], USD $)	1 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Debt instrument face amount	$ 70,000,000
Credit facilities, amount outstanding		105,000,000	125,000,000
Credit facility, maturity date	2015-10
Debt instrument, basis spread of interest rate		2.85%	2.85%
Revolving facility agreement, availability		295,000,000
Credit facilities, weighted average interest rate		3.20%	3.20%
Federal Funds Rate [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread of interest rate	0.50%
Minimum [Member]
Debt Instrument [Line Items]
Credit facilities, amount outstanding	330,000,000
Debt instrument, basis spread of interest rate	1.60%
Credit facilities, percentage of commitment fee on unused capacity	0.375%
Minimum [Member] | London Interbank Offered Rate [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread of interest rate	2.60%
Maximum [Member]
Debt Instrument [Line Items]
Credit facilities, amount outstanding	$ 400,000,000
Debt instrument, basis spread of interest rate	2.40%
Credit facilities, percentage of commitment fee on unused capacity	0.50%
Maximum [Member] | London Interbank Offered Rate [Member]
Debt Instrument [Line Items]
Debt instrument, basis spread of interest rate	3.40%