Interim Consolidated Financial Statements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2014 Depreciation Expenses [Member]	Mar. 31, 2014 Other Immaterial Expenses [Member]	Mar. 31, 2013 Adjustments To Gains Losses On Investments [Member]	Mar. 31, 2013 Adjustments Related to Insignificant Variances in Deferred Revenue [Member]
Out-of-period adjustments	$ 0.5	$ 0.4	$ 0.1
Adjustments related to prior period				$ (0.1)	$ (0.1)
Revised Consolidated Statements of Comprehensive Income Description	The consolidated statement of comprehensive income for the three months ended March 31, 2013 is impacted by the same amount as net income for the period.

- Definition

Description of a prior period adjustment to previously issued financial statements, including an adjustment that is a correction of an error. At a minimum, the description may include the nature and reasons for the adjustment and the periods affected by the adjustment, as well as (1) the effect of the correction on each financial statement line item and any per-share amounts affected for each prior period presented (2) the cumulative effect of the change on retained earnings or other appropriate components of equity or net assets in the statement of financial position, as of the beginning of the earliest period presented, and (3) the effect of the prior period adjustment (both gross and net of applicable income tax) on the net income of each prior period presented in the entity's annual report for the year in which the adjustments are made.

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