Investment Securities - Schedule of Investment Securities' Gross Unrealized Losses and Fair Value by Investment Category (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	$ 522,016	$ 550,952
Available-for-sale securities, Less than 12 months, Unrealized Loss	13,556	15,091
Available-for-sale securities, 12 months or longer, Fair Value	4,239	4,654
Available-for-sale securities, 12 months or longer, Unrealized Loss	95	90
Available-for-sale securities, Total, Fair Value	526,255	555,606
Available-for-sale securities, Total, Unrealized Loss	13,651	15,181
Held-to-maturity, Less than 12 months, Fair Value	84,121	112,642
Held-to-maturity, Less than 12 months, Unrealized Loss	969	1,374
Held-to-maturity, 12 months or longer, Fair Value	1,960	695
Held-to-maturity, 12 months or longer, Unrealized Loss	47	11
Held-to-maturity, Total, Fair Value	86,081	113,337
Held-to-maturity, Total, Unrealized Loss	1,016	1,385
CMO
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	161,225	160,572
Available-for-sale securities, Less than 12 months, Unrealized Loss	3,469	3,867
Available-for-sale securities, 12 months or longer, Fair Value	4,239	4,654
Available-for-sale securities, 12 months or longer, Unrealized Loss	95	90
Available-for-sale securities, Total, Fair Value	165,464	165,226
Available-for-sale securities, Total, Unrealized Loss	3,564	3,957
FNMA MBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	276,175	50,878
Available-for-sale securities, Less than 12 months, Unrealized Loss	8,289	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	276,175	50,878
Available-for-sale securities, Total, Unrealized Loss	8,289	1,330
FHLMC MBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	41,765	300,403
Available-for-sale securities, Less than 12 months, Unrealized Loss	1,261	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	41,765	300,403
Available-for-sale securities, Total, Unrealized Loss	1,261	9,404
GNMA MBS
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	16,236	16,480
Available-for-sale securities, Less than 12 months, Unrealized Loss	445	427
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	16,236	16,480
Available-for-sale securities, Total, Unrealized Loss	445	427
Other investments
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	634	623
Available-for-sale securities, Less than 12 months, Unrealized Loss	20	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	634	623
Available-for-sale securities, Total, Unrealized Loss	20	3
GSE
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, Less than 12 months, Fair Value	25,981	21,996
Available-for-sale securities, Less than 12 months, Unrealized Loss	72	60
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	25,981	21,996
Available-for-sale securities, Total, Unrealized Loss	72	60
State and political subdivisions
Schedule of Available-for-sale Securities [Line Items]
Held-to-maturity, Less than 12 months, Fair Value	84,121	112,642
Held-to-maturity, Less than 12 months, Unrealized Loss	969	1,374
Held-to-maturity, 12 months or longer, Fair Value	1,960	695
Held-to-maturity, 12 months or longer, Unrealized Loss	47	11
Held-to-maturity, Total, Fair Value	86,081	113,337
Held-to-maturity, Total, Unrealized Loss	$ 1,016	$ 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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27290-111563

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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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