Goodwill and Acquired Intangibles - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Intangible Assets And Goodwill [Line Items]
Amortization expense of acquired intangibles	$ 1.9	$ 1.7	$ 1.5
Accumulated amortization of intangibles	29.4	27.5
Maximum
Intangible Assets And Goodwill [Line Items]
Expected amortization expense in 2014	2.8
Expected amortization expense in 2015	2.8
Expected amortization expense in 2016	2.8
Expected amortization expense in 2017	2.8
Expected amortization expense in 2018	$ 2.8