Goodwill and Intangible Assets - Finite-Lived Intangible Assets, Net of Accumulated Amortization (Parenthetical) (Detail)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Goodwill [Line Items]
Weighted average useful life	7 years	10 years
Trading rights [Member]
Goodwill [Line Items]
Amortization period, in years	9 years	10 years
Technology [Member]
Goodwill [Line Items]
Amortization period, in years	5 years	3 years
Customer and broker relationships [Member]
Goodwill [Line Items]
Amortization period, in years	10 years
Trade names [Member]
Goodwill [Line Items]
Amortization period, in years	10 years