Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)	$ 81,187	$ 77,996	$ 79,191	$ 79,050	$ 84,361	$ 74,150	$ 75,973	$ 74,273	$ 317,424	$ 308,757	$ 272,873
Net periodic pension cost									7,363	(1,529)	(8,567)
Impairment losses									(1,000)	(1,414)	(1,409)	(3,927)	(24,795)
Tax (expense) or benefit	(10,602)	(6,869)	(13,734)	(10,392)	(11,020)	(5,861)	(10,889)	(8,340)	(41,597)	(36,110)	(27,302)
Net Income	24,549	23,948	28,478	23,945	23,009	19,737	27,206	21,723	100,920	91,675	72,460
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income									(4,105)	7,057
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Unrealized Gains and Losses on Available-for-Sale Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net securities gains									4,341	15,052
Impairment losses									(1,000)	(1,414)
Total before tax									3,341	13,638
Tax (expense) or benefit									(1,137)	(5,272)
Net Income									2,204	8,366
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Unrealized Gains Losses on Held-to-Maturity Securities [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)									(225)	870
Tax (expense) or benefit									37	(348)
Net Income									(188)	522
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Gains and Losses on Cash Flow Hedges [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax (expense) or benefit										(95)
Net Income										145
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Gains and Losses on Cash Flow Hedges [Member] | Interest Rate Contract [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income/(expense)										240
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member] | Accumulated Defined Benefit Pensions Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net periodic pension cost									(10,337)	(3,294)
Tax (expense) or benefit									4,216	1,318
Net Income									$ (6,121)	$ (1,976)