Long-Term Borrowings - Summary of Subordinated Debentures (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Carrying Amount	$ 86,328,000	$ 85,777,000
3 Month LIBOR | Subordinated Debt With 4 Point 20 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	3.58%
3 Month LIBOR | Subordinated Debt With 4 Point 20 Percent Interest Rate Two
Debt Instrument [Line Items]
Interest Rate, Basis Points	3.58%
3 Month LIBOR | Subordinated Debt With 3 Point 73 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	3.10%
3 Month LIBOR | Subordinated Debt With 3 Point 47 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	2.85%
3 Month LIBOR | Subordinated Debt With 3 Point 47 Percent Interest Rate Two
Debt Instrument [Line Items]
Interest Rate, Basis Points	2.85%
3 Month LIBOR | Subordinated Debt With 2 Point 31 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	1.68%
3 Month LIBOR | Subordinated Debt With 2 Point 03 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	1.40%
3 Month LIBOR | Subordinated Debt With 2 Point 17 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	1.54%
3 Month LIBOR | Subordinated Debt With 2 Point 17 Percent Interest Rate Two
Debt Instrument [Line Items]
Interest Rate, Basis Points	1.55%
3 Month LIBOR | Subordinated Debt With 2 Point 84 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	1.65%
3 Month LIBOR | Subordinated Debt With 2 Point 07 Percent Interest Rate
Debt Instrument [Line Items]
Interest Rate, Basis Points	1.43%
Subordinated Debt
Debt Instrument [Line Items]
Face Amount	$ 151,000,000
Carrying Amount	$ 86,328,000	85,777,000
Subordinated Debt | Subordinated Debt With 4 Point 20 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Jul. 31, 2001
Face Amount	$ 5,000,000
Carrying Amount	$ 3,973,000	3,959,000
Interest Rate	4.20%
Maturity Date	Jul. 31, 2031
Subordinated Debt | Subordinated Debt With 4 Point 20 Percent Interest Rate Two
Debt Instrument [Line Items]
Date of Offering	Jul. 31, 2001
Face Amount	$ 4,000,000
Carrying Amount	$ 2,781,000	2,764,000
Interest Rate	4.20%
Maturity Date	Jul. 31, 2031
Subordinated Debt | Subordinated Debt With 3 Point 73 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Jun. 26, 2003
Face Amount	$ 10,000,000
Carrying Amount	$ 6,147,000	6,120,000
Interest Rate	3.73%
Maturity Date	Jun. 26, 2033
Subordinated Debt | Subordinated Debt With 3 Point 47 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Sep. 25, 2003
Face Amount	$ 10,000,000
Carrying Amount	$ 6,706,000	6,668,000
Interest Rate	3.47%
Maturity Date	Oct. 08, 2033
Subordinated Debt | Subordinated Debt With 3 Point 47 Percent Interest Rate Two
Debt Instrument [Line Items]
Date of Offering	Dec. 30, 2003
Face Amount	$ 10,000,000
Carrying Amount	$ 5,934,000	5,906,000
Interest Rate	3.47%
Maturity Date	Dec. 30, 2033
Subordinated Debt | Subordinated Debt With 2 Point 31 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Jun. 28, 2005
Face Amount	$ 3,000,000
Carrying Amount	$ 1,658,000	1,645,000
Interest Rate	2.31%
Maturity Date	Jun. 28, 2035
Subordinated Debt | Subordinated Debt With 2 Point 03 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Dec. 22, 2005
Face Amount	$ 10,000,000
Carrying Amount	$ 4,763,000	4,731,000
Interest Rate	2.03%
Maturity Date	Mar. 15, 2036
Subordinated Debt | Subordinated Debt With 2 Point 17 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Dec. 28, 2005
Face Amount	$ 13,000,000
Carrying Amount	$ 6,939,000	6,884,000
Interest Rate	2.17%
Maturity Date	Mar. 15, 2036
Subordinated Debt | Subordinated Debt With 2 Point 17 Percent Interest Rate Two
Debt Instrument [Line Items]
Date of Offering	Jun. 23, 2006
Face Amount	$ 20,000,000
Carrying Amount	$ 11,862,000	11,786,000
Interest Rate	2.17%
Maturity Date	Jul. 07, 2036
Subordinated Debt | Subordinated Debt With 2 Point 84 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	May 16, 2007
Face Amount	$ 56,000,000
Carrying Amount	$ 30,006,000	29,782,000
Interest Rate	2.84%
Maturity Date	Jun. 15, 2037
Subordinated Debt | Subordinated Debt With 2 Point 07 Percent Interest Rate
Debt Instrument [Line Items]
Date of Offering	Jun. 15, 2007
Face Amount	$ 10,000,000
Carrying Amount	$ 5,559,000	$ 5,532,000
Interest Rate	2.07%
Maturity Date	Sep. 06, 2037