Summary of Significant Accounting Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Cash, cash equivalents and marketable securities	122.7
Reverse stock split	ten-for-one
Reverse stock split effective date	Nov. 07, 2014
Number of operating segment	1
United States
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Percentage of revenue earned	96.00%	89.00%	88.00%
Percentage of long lived assets	11.00%	9.00%
Maximum
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Cash equivalents original maturity period	3 months
Rhein
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]
Currency translation adjustments	(1.6)	0.5	0.4
Currency transaction gain (loss)	0.4	(0.2)	(0.2)