Employee Benefit Plans - Fair Value of Total Plan Assets by Major Asset Category (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	$ 81,130	$ 76,710	$ 64,390
(Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	81,130	76,710
(Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
(Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	995	934
Cash and cash equivalents [Member] | (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	995	934
Cash and cash equivalents [Member] | (Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Cash and cash equivalents [Member] | (Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Fixed income securities [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	9,258	12,596
Fixed income securities [Member] | (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	9,258	12,596
Fixed income securities [Member] | (Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Fixed income securities [Member] | (Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Domestic large cap [Member] | Equity securities [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	45,137	40,669
Domestic large cap [Member] | Equity securities [Member] | (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	45,137	40,669
Domestic large cap [Member] | Equity securities [Member] | (Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Domestic large cap [Member] | Equity securities [Member] | (Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Mid cap value/growth [Member] | Equity securities [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	13,725	12,610
Mid cap value/growth [Member] | Equity securities [Member] | (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	13,725	12,610
Mid cap value/growth [Member] | Equity securities [Member] | (Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Mid cap value/growth [Member] | Equity securities [Member] | (Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Small cap value/growth [Member] | Equity securities [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	7,894	7,163
Small cap value/growth [Member] | Equity securities [Member] | (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	7,894	7,163
Small cap value/growth [Member] | Equity securities [Member] | (Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Small cap value/growth [Member] | Equity securities [Member] | (Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Foreign equities [Member] | Equity securities [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	4,121	2,738
Foreign equities [Member] | Equity securities [Member] | (Level 1) Quoted Prices in Active Markets for Identical Assets [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	4,121	2,738
Foreign equities [Member] | Equity securities [Member] | (Level 2) Significant Other Observable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	0	0
Foreign equities [Member] | Equity securities [Member] | (Level 3) Significant Unobservable Inputs [Member]
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of plan assets	$ 0	$ 0