Accumulated Other Comprehensive Income (Loss) - Schedule of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (31,555)	$ (44,466)
Other comprehensive income (loss) before reclassifications	8,026	6,215
Amounts reclassified from accumulated other comprehensive income (loss)	(713)	321
Other comprehensive income (loss), net of tax	7,313	6,536
Ending Balance	(24,242)	(37,930)
Accumulated Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(748)	(21,108)
Other comprehensive income (loss) before reclassifications	11,515	7,415
Amounts reclassified from accumulated other comprehensive income (loss)	(1,688)	(282)
Other comprehensive income (loss), net of tax	9,827	7,133
Ending Balance	9,079	(13,975)
Accumulated Unrealized Gains Losses on Held-to-Maturity Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(15,776)	(16,767)
Amounts reclassified from accumulated other comprehensive income (loss)	403	270
Other comprehensive income (loss), net of tax	403	270
Ending Balance	(15,373)	(16,497)
Accumulated Gains and Losses on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(5,935)	(190)
Other comprehensive income (loss) before reclassifications	(3,489)	(1,200)
Amounts reclassified from accumulated other comprehensive income (loss)	115
Other comprehensive income (loss), net of tax	(3,374)	(1,200)
Ending Balance	(9,309)	(1,390)
Accumulated Defined Benefit Pensions Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(9,096)	(6,401)
Amounts reclassified from accumulated other comprehensive income (loss)	457	333
Other comprehensive income (loss), net of tax	457	333
Ending Balance	$ (8,639)	$ (6,068)