Derivatives - Fair Value of Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified					9 Months Ended				9 Months Ended				9 Months Ended				9 Months Ended				9 Months Ended			9 Months Ended			3 Months Ended
	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2014 Interest Rate Swaps [Member]		Dec. 31, 2013 Interest Rate Swaps [Member]		Sep. 30, 2014 Interest Rate Swaps Two [Member]		Dec. 31, 2013 Interest Rate Swaps Two [Member]		Sep. 30, 2014 Interest Rate Swaps Three [Member]		Dec. 31, 2013 Interest Rate Swaps Three [Member]		Sep. 30, 2014 Interest Rate Swaps Four [Member]		Dec. 31, 2013 Interest Rate Swaps Four [Member]		Sep. 30, 2014 Interest Rate Swaps Five [Member]		Dec. 31, 2013 Interest Rate Swaps Five [Member]	Sep. 30, 2014 Interest Rate Swaps Six [Member]		Dec. 31, 2013 Interest Rate Swaps Six [Member]	Sep. 30, 2014 Interest Rate Swaps Nine [Member]		Sep. 30, 2014 Interest Rate Swap Ten [Member]		Sep. 30, 2014 Interest Rate Swap Eleven [Member]		Sep. 30, 2014 Interest Rate Swap Twelve [Member]		Sep. 30, 2014 Interest Rate Swap Seven [Member]		Sep. 30, 2014 Interest Rate Swap Eight [Member]
Derivative Instruments, Gain (Loss) [Line Items]
(in millions of dollars) Notional Value					$ 25.0				$ 28.1				$ 34.2				$ 7.6				$ 55.0			$ 48.0			$ 20.0		$ 20.0		$ 20.0		$ 20.0		$ 30.0		$ 20.0
Fair Value at period end	$ (1.1)	[1]	$ (0.1)	[1]	$ (0.2)	[1]	$ (0.3)	[1]	$ (0.4)	[1]	$ (0.5)	[1]	$ 0.2	[1]	$ 0.2	[1]	$ 0.1	[1]	$ 0.1	[1]	$ 0.2	[1]	$ (0.2)	$ 0.2	[1]	$ (0.2)	$ (0.2)	[1]	$ (0.2)	[1]	$ (0.2)	[1]	$ (0.2)	[1]	$ (0.2)	[1]	$ (0.2)	[1]
Interest Rate					1.10%				1.38%				3.72%				1.00%				1.12%			1.12%			1.78%		1.79%		1.79%		1.79%		1.7775%		1.7775%
Maturity Date					Jul. 31, 2016				Jan. 02, 2017				Dec. 01, 2017				Jan. 01, 2018				Jan. 01, 2018			Jan. 01, 2018			Jan. 02, 2019		Jan. 02, 2019		Jan. 02, 2019		Jan. 02, 2019		Jan. 02, 2019		Jan. 02, 2019

[1] As of September 30, 2014 and December 31, 2013, derivative valuations in their entirety were classified in Level 2 of the fair value hierarchy. As of September 30, 2014 and December 31, 2013, we did not have any significant recurring fair value measurements related to derivative instruments using significant unobservable inputs (Level 3).