Commitment Fee Under Credit Facilities (Detail)	12 Months Ended
	Dec. 31, 2012
Range One
Line of Credit Facility [Line Items]
Commitment Fee	0.50%
Range Two
Line of Credit Facility [Line Items]
Commitment Fee	0.45%
Range Three
Line of Credit Facility [Line Items]
Commitment Fee	0.40%
Abr Loans | Range One
Line of Credit Facility [Line Items]
Margin on loans	1.75%
Abr Loans | Range Two
Line of Credit Facility [Line Items]
Margin on loans	1.50%
Abr Loans | Range Three
Line of Credit Facility [Line Items]
Margin on loans	1.25%
Eurodollar Loans | Range One
Line of Credit Facility [Line Items]
Margin on loans	2.75%
Eurodollar Loans | Range Two
Line of Credit Facility [Line Items]
Margin on loans	2.50%
Eurodollar Loans | Range Three
Line of Credit Facility [Line Items]
Margin on loans	2.25%