Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Sep. 30, 2017 USD ($) Security	Dec. 31, 2016 USD ($) Security
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	$ 273,319	$ 428,488
Available for Sale, Less Than 12 Months, Unrealized Losses	1,980	6,421
Available for Sale, 12 Months or Longer, Fair Value	124,851	20,173
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 2,863	$ 747
Available for Sale, Number of Securities | Security	131	167
Available for Sale, Total, Fair Value	$ 398,170	$ 448,661
Available for Sale, Total, Unrealized Losses	4,843	7,168
Held to Maturity, Less Than 12 Months, Fair Value	49,171	97,373
Held to Maturity, Less Than 12 Months, Unrealized Losses	441	1,393
Held to Maturity, 12 Months or Longer, Fair Value	14,885	1,462
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 559	$ 64
Held to Maturity, Number of Securities | Security	32	63
Held to Maturity, Total, Fair Value	$ 64,056	$ 98,835
Held to Maturity, Total, Unrealized Losses	1,000	1,457
US Treasury and Government Agencies [Member]
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	66,973	94,153
Available for Sale, Less Than 12 Months, Unrealized Losses	273	$ 1,280
Available for Sale, 12 Months or Longer, Fair Value	17,235
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 551
Available for Sale, Number of Securities | Security	16	18
Available for Sale, Total, Fair Value	$ 84,208	$ 94,153
Available for Sale, Total, Unrealized Losses	824	1,280
Held to Maturity, Less Than 12 Months, Fair Value	5,419	17,147
Held to Maturity, Less Than 12 Months, Unrealized Losses	14	$ 430
Held to Maturity, 12 Months or Longer, Fair Value	6,768
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 260
Held to Maturity, Number of Securities | Security	2	3
Held to Maturity, Total, Fair Value	$ 12,187	$ 17,147
Held to Maturity, Total, Unrealized Losses	274	430
Mortgage-Backed Securities, Residential [Member]
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	198,410	292,873
Available for Sale, Less Than 12 Months, Unrealized Losses	1,658	4,078
Available for Sale, 12 Months or Longer, Fair Value	85,011	15,453
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 1,662	$ 409
Available for Sale, Number of Securities | Security	85	91
Available for Sale, Total, Fair Value	$ 283,421	$ 308,326
Available for Sale, Total, Unrealized Losses	3,320	4,487
Held to Maturity, Less Than 12 Months, Fair Value	27,833	27,909
Held to Maturity, Less Than 12 Months, Unrealized Losses	309	535
Held to Maturity, 12 Months or Longer, Fair Value	7,350	1,061
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 260	$ 63
Held to Maturity, Number of Securities | Security	18	15
Held to Maturity, Total, Fair Value	$ 35,183	$ 28,970
Held to Maturity, Total, Unrealized Losses	569	598
Mortgage-Backed Securities, Multifamily [Member]
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	5,131	5,178
Available for Sale, Less Than 12 Months, Unrealized Losses	$ 36	$ 35
Available for Sale, Number of Securities | Security	1	1
Available for Sale, Total, Fair Value	$ 5,131	$ 5,178
Available for Sale, Total, Unrealized Losses	36	35
Held to Maturity, Less Than 12 Months, Fair Value	1,970	2,015
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 13	$ 44
Held to Maturity, Number of Securities | Security	2	2
Held to Maturity, Total, Fair Value	$ 1,970	$ 2,015
Held to Maturity, Total, Unrealized Losses	13	44
Obligations of States and Political Subdivisions [Member]
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value	2,805	29,904
Available for Sale, Less Than 12 Months, Unrealized Losses	13	$ 933
Available for Sale, 12 Months or Longer, Fair Value	12,936
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 264
Available for Sale, Number of Securities | Security	27	54
Available for Sale, Total, Fair Value	$ 15,741	$ 29,904
Available for Sale, Total, Unrealized Losses	277	933
Held to Maturity, Less Than 12 Months, Fair Value	13,949	50,302
Held to Maturity, Less Than 12 Months, Unrealized Losses	105	384
Held to Maturity, 12 Months or Longer, Fair Value	767	401
Held to Maturity, 12 Months or Longer, Unrealized Losses	$ 39	$ 1
Held to Maturity, Number of Securities | Security	10	43
Held to Maturity, Total, Fair Value	$ 14,716	$ 50,703
Held to Maturity, Total, Unrealized Losses	144	385
Other Debt Securities [Member]
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value		350
Available for Sale, Less Than 12 Months, Unrealized Losses		$ 1
Available for Sale, Number of Securities | Security		1
Available for Sale, Total, Fair Value		$ 350
Available for Sale, Total, Unrealized Losses		1
Equity Securities [Member]
Investment [Line Items]
Available for Sale, Less Than 12 Months, Fair Value		6,030
Available for Sale, Less Than 12 Months, Unrealized Losses		94
Available for Sale, 12 Months or Longer, Fair Value	9,669	4,720
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 386	$ 338
Available for Sale, Number of Securities | Security	2	2
Available for Sale, Total, Fair Value	$ 9,669	$ 10,750
Available for Sale, Total, Unrealized Losses	$ 386	$ 432