Investment Securities - Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category (Detail) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	$ 487,896	$ 550,952
Available-for-sale securities, Less than 12 months, Unrealized Loss	9,596	15,091
Available-for-sale securities, 12 months or longer, Fair Value	7,876	4,654
Available-for-sale securities, 12 months or longer, Unrealized Loss	146	90
Available-for-sale securities, Total, Fair Value	495,772	555,606
Available-for-sale securities, Total, Unrealized Loss	9,742	15,181
Held-to-maturity, Less than 12 months, Fair Value	32,927	112,642
Held-to-maturity, Less than 12 months, Unrealized Loss	193	1,374
Held-to-maturity, 12 months or longer, Fair Value	1,969	695
Held-to-maturity, 12 months or longer, Unrealized Loss	27	11
Held-to-maturity, Total, Fair Value	34,896	113,337
Held-to-maturity, Total, Unrealized Loss	220	1,385
CMO
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	174,552	160,572
Available-for-sale securities, Less than 12 months, Unrealized Loss	2,654	3,867
Available-for-sale securities, 12 months or longer, Fair Value	4,143	4,654
Available-for-sale securities, 12 months or longer, Unrealized Loss	54	90
Available-for-sale securities, Total, Fair Value	178,695	165,226
Available-for-sale securities, Total, Unrealized Loss	2,708	3,957
FNMA MBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	255,044	50,878
Available-for-sale securities, Less than 12 months, Unrealized Loss	5,773	1,330
Available-for-sale securities, 12 months or longer, Fair Value	0	0
Available-for-sale securities, 12 months or longer, Unrealized Loss	0	0
Available-for-sale securities, Total, Fair Value	255,044	50,878
Available-for-sale securities, Total, Unrealized Loss	5,773	1,330
FHLMC MBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	45,583	300,403
Available-for-sale securities, Less than 12 months, Unrealized Loss	839	9,404
Available-for-sale securities, 12 months or longer, Fair Value	0	0
Available-for-sale securities, 12 months or longer, Unrealized Loss	0	0
Available-for-sale securities, Total, Fair Value	45,583	300,403
Available-for-sale securities, Total, Unrealized Loss	839	9,404
GNMA MBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	12,097	16,480
Available-for-sale securities, Less than 12 months, Unrealized Loss	313	427
Available-for-sale securities, 12 months or longer, Fair Value	3,733	0
Available-for-sale securities, 12 months or longer, Unrealized Loss	92	0
Available-for-sale securities, Total, Fair Value	15,830	16,480
Available-for-sale securities, Total, Unrealized Loss	405	427
Other investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	620	623
Available-for-sale securities, Less than 12 months, Unrealized Loss	17	3
Available-for-sale securities, 12 months or longer, Fair Value	0	0
Available-for-sale securities, 12 months or longer, Unrealized Loss	0	0
Available-for-sale securities, Total, Fair Value	620	623
Available-for-sale securities, Total, Unrealized Loss	17	3
GSE
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value		21,996
Available-for-sale securities, Less than 12 months, Unrealized Loss		60
Available-for-sale securities, 12 months or longer, Fair Value		0
Available-for-sale securities, 12 months or longer, Unrealized Loss		0
Available-for-sale securities, Total, Fair Value		21,996
Available-for-sale securities, Total, Unrealized Loss		60
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity, Less than 12 months, Fair Value	32,927	112,642
Held-to-maturity, Less than 12 months, Unrealized Loss	193	1,374
Held-to-maturity, 12 months or longer, Fair Value	1,969	695
Held-to-maturity, 12 months or longer, Unrealized Loss	27	11
Held-to-maturity, Total, Fair Value	34,896	113,337
Held-to-maturity, Total, Unrealized Loss	$ 220	$ 1,385

Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale in a continuous loss position.

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