Securities - Schedule of Fair Value of Available-for-Sale and Held-to-Maturity Securities by Contractual Maturity (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule Of Available For Sale Or Held To Maturity Securities [Line Items]
Total available-for-sale securities, One Year or less	$ 11,403
Total available-for-sale securities, One to Five Years	69,029
Total available-for-sale securities, Five to Ten Years	59,782
Total available-for-sale securities, After Ten Years	85,819
Total available-for-sale securities, Mortgage-backed and Equity	780,046
Available-for-sale, Estimated Fair Value	1,006,079	934,386
Total held-to-maturity securities, One Year or less	4,743
Total held-to-maturity securities, One to Five Years	12,390
Total held-to-maturity securities, Five to Ten years	184,698
Total held-to-maturity securities, After Ten Years	334,608
Total held-to-maturity securities, Mortgage-backed and Equity	92,101
Held-to-maturity securities, Fair value	628,540	596,308
Total securities, One Year or less	16,146
Total securities, One to Five Years	81,419
Total securities, Five to Ten Years	244,480
Total securities, After Ten Years, Fair value	420,427
Total securities, Mortgage- backed and Equity	872,147
Total securities, Fair value	1,634,619
Obligations of Government Agencies [Member]
Schedule Of Available For Sale Or Held To Maturity Securities [Line Items]
Total available-for-sale securities, One Year or less	313
Total available-for-sale securities, One to Five Years	9,833
Total available-for-sale securities, Five to Ten Years	26,123
Total available-for-sale securities, After Ten Years	42,633
Available-for-sale, Estimated Fair Value	78,902	73,232
Residential Mortgage-Backed Securities and Collateralized Mortgage Obligations of Government Agencies [Member]
Schedule Of Available For Sale Or Held To Maturity Securities [Line Items]
Total available-for-sale securities, Mortgage-backed and Equity	767,482
Available-for-sale, Estimated Fair Value	767,482	694,267
Total held-to-maturity securities, Mortgage-backed and Equity	92,101
Held-to-maturity securities, Fair value	92,101	101,190
Obligations of State and Political Subdivisions [Member]
Schedule Of Available For Sale Or Held To Maturity Securities [Line Items]
Total available-for-sale securities, One Year or less	7,072
Total available-for-sale securities, One to Five Years	43,257
Total available-for-sale securities, Five to Ten Years	21,615
Total available-for-sale securities, After Ten Years	38,295
Available-for-sale, Estimated Fair Value	110,239	116,346
Total held-to-maturity securities, One Year or less	4,743
Total held-to-maturity securities, One to Five Years	12,390
Total held-to-maturity securities, Five to Ten years	178,977
Total held-to-maturity securities, After Ten Years	334,608
Held-to-maturity securities, Fair value	530,718	492,648
Corporate Debt Securities [Member]
Schedule Of Available For Sale Or Held To Maturity Securities [Line Items]
Total available-for-sale securities, One Year or less	4,018
Total available-for-sale securities, One to Five Years	15,939
Total available-for-sale securities, Five to Ten Years	12,044
Total available-for-sale securities, After Ten Years	4,891
Available-for-sale, Estimated Fair Value	36,892	38,481
Total held-to-maturity securities, Five to Ten years	5,721
Held-to-maturity securities, Fair value	5,721	2,470
Equity Securities [Member]
Schedule Of Available For Sale Or Held To Maturity Securities [Line Items]
Total available-for-sale securities, Mortgage-backed and Equity	12,564
Available-for-sale, Estimated Fair Value	$ 12,564	$ 12,060