Summary of Significant Accounting Policies - Schedule of Capitalized Software Included in Property, Plant and Equipment (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Regulatory Assets [Abstract]
Capitalized software development costs	$ 83,026	$ 77,308
Accumulated amortization	(59,257)	(53,943)
Net capitalized software development costs	$ 23,769	$ 23,365