Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Income Tax Disclosure [Abstract]
Net deferred tax asset	$ 39.7	$ 28.8
Deferred tax asset attributable to unrealized Losses	10.5
Deferred tax liability attributable to unrealized gains		2.8
Net operating loss carryforward	$ 72.9	$ 81.2