Tax Benefit Expense on Reclassifications Out of Accumulated Other Comprehensive Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax expense on gains on marketable securities reclassified into earnings	$ 2,994	$ 1,670	$ 7,274	$ 2,130
Tax expense (benefit) on gains (losses) on cash flow hedges reclassified into earnings	144	(2,627)	715	(4,125)
Tax expense (benefit) on gains (losses) on defined benefit plan reclassified into earnings	$ 8	$ (2)	$ 1	$ 1