Investment Securities - Reconciliation of Available-for-Sale and Held-to-Maturity Securities in Continuous Unrealized Loss Position (Detail) $ in Thousands	Dec. 31, 2018 USD ($) Security	Dec. 31, 2017 USD ($) Security
Investment [Line Items]
Available for Sale, Less than 12 Months, Fair Value	$ 33,973	$ 289,390
Available for Sale, Less than 12 Months, Unrealized Losses	278	2,446
Available for Sale, 12 Months or Longer, Fair Value	476,622	230,566
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 11,923	$ 5,588
Available for Sale, Number of Securities | Security	220	185
Available for Sale, Total, Fair Value	$ 510,595	$ 519,956
Available for Sale, Total, Unrealized Losses	12,201	8,034
Held to Maturity, Less Than 12 Months, Fair Value	13,971
Held to Maturity, Less Than 12 Months, Unrealized Losses	185
Held to Maturity, 12 Months or Longer, Fair Value	103,507
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 2,811
Held to Maturity, Number of Securities | Security	72
Held to Maturity, Fair Value	$ 117,478
Held to Maturity, Unrealized Losses	2,996
Obligations of states and political subdivisions
Investment [Line Items]
Available for Sale, Less than 12 Months, Fair Value	1,289	9,612
Available for Sale, Less than 12 Months, Unrealized Losses	2	77
Available for Sale, 12 Months or Longer, Fair Value	26,522	12,970
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 584	$ 340
Available for Sale, Number of Securities | Security	50	39
Available for Sale, Total, Fair Value	$ 27,811	$ 22,582
Available for Sale, Total, Unrealized Losses	586	417
Held to Maturity, Less Than 12 Months, Fair Value	1,764	15,353
Held to Maturity, Less Than 12 Months, Unrealized Losses	8	56
Held to Maturity, 12 Months or Longer, Fair Value	15,580	6,028
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 320	$ 132
Held to Maturity, Number of Securities | Security	27	23
Held to Maturity, Fair Value	$ 17,344	$ 21,381
Held to Maturity, Unrealized Losses	328	188
Mortgage-backed securities, multifamily
Investment [Line Items]
Available for Sale, Less than 12 Months, Fair Value	1,977	0
Available for Sale, Less than 12 Months, Unrealized Losses	2	0
Available for Sale, 12 Months or Longer, Fair Value	12,911	5,088
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 202	$ 63
Available for Sale, Number of Securities | Security	4	1
Available for Sale, Total, Fair Value	$ 14,888	$ 5,088
Available for Sale, Total, Unrealized Losses	204	63
Held to Maturity, Less Than 12 Months, Fair Value	0	1,935
Held to Maturity, Less Than 12 Months, Unrealized Losses	0	22
Held to Maturity, 12 Months or Longer, Fair Value	1,818	0
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 35	$ 0
Held to Maturity, Number of Securities | Security	2	2
Held to Maturity, Fair Value	$ 1,818	$ 1,935
Held to Maturity, Unrealized Losses	35	22
Mortgage-backed securities, residential
Investment [Line Items]
Available for Sale, Less than 12 Months, Fair Value	10,119	199,387
Available for Sale, Less than 12 Months, Unrealized Losses	58	1,723
Available for Sale, 12 Months or Longer, Fair Value	316,851	157,739
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 8,785	$ 4,040
Available for Sale, Number of Securities | Security	139	118
Available for Sale, Total, Fair Value	$ 326,970	$ 357,126
Available for Sale, Total, Unrealized Losses	8,843	5,763
Held to Maturity, Less Than 12 Months, Fair Value	8,325	26,090
Held to Maturity, Less Than 12 Months, Unrealized Losses	59	426
Held to Maturity, 12 Months or Longer, Fair Value	53,761	19,203
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 1,779	$ 552
Held to Maturity, Number of Securities | Security	36	25
Held to Maturity, Fair Value	$ 62,086	$ 45,293
Held to Maturity, Unrealized Losses	1,838	978
U.S. Treasury and U.S. government agencies
Investment [Line Items]
Available for Sale, Less than 12 Months, Fair Value	20,588	80,391
Available for Sale, Less than 12 Months, Unrealized Losses	216	646
Available for Sale, 12 Months or Longer, Fair Value	120,338	54,769
Available for Sale, 12 Months or Longer, Unrealized Losses	$ 2,352	$ 1,145
Available for Sale, Number of Securities | Security	27	27
Available for Sale, Total, Fair Value	$ 140,926	$ 135,160
Available for Sale, Total, Unrealized Losses	2,568	1,791
Held to Maturity, Less Than 12 Months, Fair Value	0	15,371
Held to Maturity, Less Than 12 Months, Unrealized Losses	0	95
Held to Maturity, 12 Months or Longer, Fair Value	32,348	6,720
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 677	$ 307
Held to Maturity, Number of Securities | Security	6	4
Held to Maturity, Fair Value	$ 32,348	$ 22,091
Held to Maturity, Unrealized Losses	677	402
Debt securities
Investment [Line Items]
Held to Maturity, Less Than 12 Months, Fair Value	3,882	58,749
Held to Maturity, Less Than 12 Months, Unrealized Losses	118	599
Held to Maturity, 12 Months or Longer, Fair Value	0	31,951
Held to Maturity, Less Than 12 Months, Unrealized Losses	$ 0	$ 991
Held to Maturity, Number of Securities | Security	1	54
Held to Maturity, Fair Value	$ 3,882	$ 90,700
Held to Maturity, Unrealized Losses	$ 118	$ 1,590