Reconciliation Between U.S. Federal Statutory Rate and Effective Rate (Detail)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
Statutory federal income tax rate	35.00%	34.00%	34.00%
State tax expense, net of federal benefit	6.40%	5.70%	7.80%
Permanent items, including nondeductible expenses	0.90%	0.90%	2.20%
State investment tax credit	(0.20%)	(0.20%)	(0.80%)
Federal, state and foreign research and development credits	(1.20%)	(0.40%)	(2.50%)
Foreign rate differential	2.50%	0.90%	2.60%
Domestic production deduction	(3.60%)	(2.30%)	(2.10%)
Effective income tax rate	39.80%	38.60%	41.20%