Components of Accumulated Other Comprehensive (Loss) Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended				3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss)	Sep. 30, 2012 Accumulated Net Unrealized Investment Gain (Loss)	Sep. 30, 2013 Accumulated Net Unrealized Investment Gain (Loss)	Sep. 30, 2012 Accumulated Net Unrealized Investment Gain (Loss)	Sep. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges	Jun. 30, 2013 Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges	Sep. 30, 2013 Accumulated Defined Benefit Plans Adjustment	Sep. 30, 2012 Accumulated Defined Benefit Plans Adjustment	Sep. 30, 2013 Accumulated Defined Benefit Plans Adjustment	Sep. 30, 2012 Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (11,105)	$ (9,878)	$ (10,078)	$ (11,365)	$ (123)	$ 2,735	$ 3,164	$ 1,792	$ (24)	$ 577	$ (11,559)	$ (12,613)	$ (13,218)	$ (13,157)
Net change	296	1,223	(731)	2,710	50	951	(3,237)	1,894	601		246	272	1,905	816
Ending balance	$ (10,809)	$ (8,655)	$ (10,809)	$ (8,655)	$ (73)	$ 3,686	$ (73)	$ 3,686	$ 577	$ 577	$ (11,313)	$ (12,341)	$ (11,313)	$ (12,341)