Other Comprehensive Income (Schedule of Accumulated Other Comprehensive Income, Net of Tax) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	$ 141,814	$ 140,434	$ 238,048
Other comprehensive income (loss) before reclassification	(27,906)	21,298	(75,195)
Amounts reclassified from accumulated other comprehensive income (loss)	(45)	(19,918)	(22,419)
Net other comprehensive income (loss) during period	(27,951)	1,380	(97,614)
Ending Balance	113,863	141,814	140,434
Securities Available For Sale [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	190,589	146,672	245,539
Other comprehensive income (loss) before reclassification	(29,933)	43,942	(98,103)
Amounts reclassified from accumulated other comprehensive income (loss)	(45)	(25)	(764)
Net other comprehensive income (loss) during period	(29,978)	43,917	(98,867)
Ending Balance	160,611	190,589	146,672
Defined Benefit Plans [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	(48,775)	(26,131)	(49,071)
Other comprehensive income (loss) before reclassification	2,027	(22,644)	22,940
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0
Net other comprehensive income (loss) during period	2,027	(22,644)	22,940
Ending Balance	(46,748)	(48,775)	(26,131)
Derivatives [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance	0	19,893	41,580
Other comprehensive income (loss) before reclassification	0	0	(32)
Amounts reclassified from accumulated other comprehensive income (loss)	0	(19,893)	(21,655)
Net other comprehensive income (loss) during period	0	(19,893)	(21,687)
Ending Balance	$ 0	$ 0	$ 19,893