Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Stockholders Equity Note [Line Items]
Amount reclassified out of accumulated comprehensive income for realized gains on available-for-sale securities		[1]
Stock-based compensation expense	5.8		5.9
Stock-based compensation expense realized tax benefits from the excess of deductible amounts over expense recognized	$ 0.6		$ 0.8
Additional common shares issued under deferred and stock compensation arrangements	336,827

[1] All amounts are net of tax. Amounts in parentheses indicate reductions in the AOCI component of stockholders' equity.