Income Tax - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Excess tax benefit from exercises of share-based arrangements	$ 19,402,000	$ 28,207,000	$ 8,764,000
Deferred tax assets, valuation allowance	0
Income tax examination, year under examination	2012
Income taxes, net of refunds	10,200,000	9,300,000	13,100,000
Stock Option Plan [Member]
Income Tax Contingency [Line Items]
Excess tax benefit from exercises of share-based arrangements	19,400,000	28,200,000
Federal Income Tax [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforwards for federal income tax	$ (650,000)