Accumulated Other Comprehensive Loss, Net of Tax (Schedule of Other Comprehensive Income (Loss)) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ (77,027)	$ (70,397)	$ (76,993)	$ (78,106)
OCI/OCL before reclassifications	2,728	10,566	564	15,728
Amounts reclassified from AOCL	2,217	2,320	4,347	4,867
Other comprehensive income (loss), net of tax	(4,945)	(12,886)	(4,911)	(20,595)
Ending balance	(72,082)	(57,511)	(72,082)	(57,511)
Available For Sale and Transferred Securities [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(17,701)	1,098	(15,476)	(6,407)
OCI/OCL before reclassifications	3,200	11,324	975	18,938
Amounts reclassified from AOCL	0	(59)	0	(168)
Other comprehensive income (loss), net of tax	(3,200)	(11,265)	(975)	(18,770)
Ending balance	(14,501)	12,363	(14,501)	12,363
Derivative Instruments [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(15,909)	(23,932)	(17,068)	(22,980)
OCI/OCL before reclassifications	(472)	(758)	(411)	(3,210)
Amounts reclassified from AOCL	1,123	1,284	2,221	2,784
Other comprehensive income (loss), net of tax	(651)	(526)	(1,810)	426
Ending balance	(15,258)	(23,406)	(15,258)	(23,406)
Defined Benefit Pension and Other Postretirement Benefit Plans [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(43,417)	(47,563)	(44,449)	(48,719)
OCI/OCL before reclassifications	0	0	0	0
Amounts reclassified from AOCL	1,094	1,095	2,126	2,251
Other comprehensive income (loss), net of tax	(1,094)	(1,095)	(2,126)	(2,251)
Ending balance	$ (42,323)	$ (46,468)	$ (42,323)	$ (46,468)