Investment Securities - Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 653,474	$ 680,191
Less than 12 months, Unrealized Loss	17,108	30,443
12 months or longer, Fair Value	87,329	67,527
12 months or longer, Unrealized Loss	4,363	4,311
Total, Fair Value	740,803	747,718
Total, Unrealized Loss	21,471	34,754
Collateralized Mortgage Obligation ("CMO") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	82,229	73,109
Less than 12 months, Unrealized Loss	2,719	4,173
12 months or longer, Fair Value	25,974	21,590
12 months or longer, Unrealized Loss	1,265	1,362
Total, Fair Value	108,203	94,699
Total, Unrealized Loss	3,984	5,535
Federal National Mortgage Association ("FNMA") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	341,483	346,266
Less than 12 months, Unrealized Loss	8,989	14,386
12 months or longer, Fair Value	17,955	17,800
12 months or longer, Unrealized Loss	1,015	1,415
Total, Fair Value	359,438	364,066
Total, Unrealized Loss	10,004	15,801
Federal Home Loan Mortgage Corporation ("FHLMC") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	116,004	116,732
Less than 12 months, Unrealized Loss	2,700	4,548
12 months or longer, Fair Value	11,593	7,307
12 months or longer, Unrealized Loss	701	446
Total, Fair Value	127,597	124,039
Total, Unrealized Loss	3,401	4,994
Government National Mortgage Association ("GNMA") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	65,773	57,076
Less than 12 months, Unrealized Loss	966	1,897
12 months or longer, Fair Value	18,433	18,829
12 months or longer, Unrealized Loss	621	1,084
Total, Fair Value	84,206	75,905
Total, Unrealized Loss	1,587	2,981
State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	42,003	83,036
Less than 12 months, Unrealized Loss	1,722	5,426
12 months or longer, Fair Value	13,374
12 months or longer, Unrealized Loss	761
Total, Fair Value	55,377	83,036
Total, Unrealized Loss	2,483	5,426
U.S. Government and government sponsored enterprises ("GSE") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	5,982	3,972
Less than 12 months, Unrealized Loss	12	13
12 months or longer, Fair Value		2,001
12 months or longer, Unrealized Loss		4
Total, Fair Value	5,982	5,973
Total, Unrealized Loss	$ 12	$ 17