Revolving Line of Credit - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Oct. 31, 2011	Aug. 02, 2007
Credit Facilities [Line Items]
Borrowing capacity under revolving line of credit	$ 150	$ 150	$ 100	$ 30
Further increases in total commitment		175
Amount outstanding on line of credit	71.3	70.4
Available on revolving line of credit	78.7
Maturity date of the facility	Dec. 21, 2016
Line of credit facility outstanding LIBOR loan amount	65.0
Line of credit facility outstanding Base Rate Loan amount	6.3
Qualified lease receivables eligible under the borrowing base computation	127.8
Minimum [Member]
Credit Facilities [Line Items]
Borrowing capacity under revolving line of credit		100
Interest rate on loans	2.90%
Maximum [Member]
Credit Facilities [Line Items]
Borrowing capacity under revolving line of credit		$ 150
Interest rate on loans	4.00%