Accumulated Other Comprehensive Loss - Schedule of Accumulated Other Comprehensive Loss (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Interest and dividends on investment	$ 198	$ 190	$ 506	$ 378
Interest expense	(40,791)	(42,110)	(119,550)	(127,590)
Amortization of prior service cost	0	(1,530)	0	(5,573)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(10,654)	(7,143)	(23,235)	(30,918)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Interest expense	(1,674)	(1,637)	(4,986)	(5,231)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	(834)	(1,177)	(2,668)	(2,495)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Unrealized Gains and Losses on Available for Sale (AFS) Securities [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Gains on securities transactions, net	103	9	102	4,008
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(43)	(3)	(43)	(1,678)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	60	6	59	2,330
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Non-Credit Impairment Losses on AFS Securities [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Interest and dividends on investment	198	190	506	378
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	(83)	(80)	(212)	(159)
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	115	110	294	219
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Unrealized Losses on Derivatives (Cash Flow Hedges) Before Tax [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Interest expense	(1,674)	(1,637)	(4,986)	(5,231)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	701	687	2,075	2,195
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	(973)	(950)	(2,911)	(3,036)
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Defined Benefit Pension Plans [Member]
Reclassification Out Of Accumulated Other Comprehensive Loss [LineItems]
Amortization of prior service cost	0	(229)	0	(672)
Amortization of net actuarial loss	(63)	(357)	(187)	(1,962)
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Settlements and Curtailments	0		0	(750)
Total before tax	(63)	(586)	(187)	(3,384)
Amounts Reclassified from Accumulated Other Comprehensive Loss, tax effect	27	243	77	1,376
Amounts Reclassified from Accumulated Other Comprehensive Loss, net of tax	$ (36)	$ (343)	$ (110)	$ (2,008)