Investment Securities - Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	$ 64,169	$ 680,191
Less than 12 months, Unrealized Loss	302	30,443
12 months or longer, Fair Value	461,075	67,527
12 months or longer, Unrealized Loss	8,364	4,311
Total, Fair Value	525,244	747,718
Total, Unrealized Loss	8,666	34,754
Collateralized Mortgage Obligation ("CMO") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	16,488	73,109
Less than 12 months, Unrealized Loss	23	4,173
12 months or longer, Fair Value	73,140	21,590
12 months or longer, Unrealized Loss	2,162	1,362
Total, Fair Value	89,628	94,699
Total, Unrealized Loss	2,185	5,535
Federal National Mortgage Association ("FNMA") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	27,205	346,266
Less than 12 months, Unrealized Loss	234	14,386
12 months or longer, Fair Value	195,763	17,800
12 months or longer, Unrealized Loss	3,137	1,415
Total, Fair Value	222,968	364,066
Total, Unrealized Loss	3,371	15,801
Federal Home Loan Mortgage Corporation ("FHLMC") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	3,798	116,732
Less than 12 months, Unrealized Loss	6	4,548
12 months or longer, Fair Value	96,077	7,307
12 months or longer, Unrealized Loss	1,400	446
Total, Fair Value	99,875	124,039
Total, Unrealized Loss	1,406	4,994
Government National Mortgage Association ("GNMA") [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value		57,076
Less than 12 months, Unrealized Loss		1,897
12 months or longer, Fair Value	52,020	18,829
12 months or longer, Unrealized Loss	525	1,084
Total, Fair Value	52,020	75,905
Total, Unrealized Loss	525	2,981
State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 months, Fair Value	5,727	83,036
Less than 12 months, Unrealized Loss	19	5,426
12 months or longer, Fair Value	44,075
12 months or longer, Unrealized Loss	1,140
Total, Fair Value	49,802	83,036
Total, Unrealized Loss	1,159	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	10,951	3,972
Less than 12 months, Unrealized Loss	20	13
12 months or longer, Fair Value		2,001
12 months or longer, Unrealized Loss		4
Total, Fair Value	10,951	5,973
Total, Unrealized Loss	$ 20	$ 17