Accumulated Other Comprehensive Loss - Schedule of Changes in Accumulated Other Comprehensive Loss After Tax (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
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance			$ (50,909)
Total other comprehensive income	8,474	5,225	11,757	18,574
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(39,152)		(39,152)
Unrealized Gains and Losses on Available for Sale (AFS) Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(2,080)		906
Other comprehensive income before reclassifications	(16,353)		(17,040)
Amounts reclassified from other comprehensive income	(25)		(2,324)
Total other comprehensive income	(16,378)		(19,364)
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(18,458)		(18,458)
Non-credit Impairment Losses on AFS Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	502		(4,175)
Other comprehensive income before reclassifications	2,008		6,751
Amounts reclassified from other comprehensive income	(43)		(109)
Total other comprehensive income	1,965		6,642
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	2,467		2,467
Unrealized Gains and Losses on Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(11,662)		(12,676)
Other comprehensive income before reclassifications	2,036		1,959
Amounts reclassified from other comprehensive income	995		2,086
Total other comprehensive income	3,031		4,045
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(8,631)		(8,631)
Defined Benefit Pension Plan [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(34,386)		(34,964)
Other comprehensive income before reclassifications	18,784		18,769
Amounts reclassified from other comprehensive income	1,072		1,665
Total other comprehensive income	19,856		20,434
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	(14,530)		(14,530)
Total Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total Accumulated Other Comprehensive Income (Loss), Beginning Balance	(47,626)		(50,909)
Other comprehensive income before reclassifications	6,475		10,439
Amounts reclassified from other comprehensive income	1,999		1,318
Total other comprehensive income	8,474		11,757
Total Accumulated Other Comprehensive Income (Loss), Ending Balance	$ (39,152)		$ (39,152)