Schedule of Market Values of Pension Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 106,839	$ 116,697	$ 106,469
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	106,839	116,697
Cash | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	612	512
Cash | Fair Value, Inputs, Level 2 | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	612	512
U.S. Large Cap | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,520	9,212
U.S. Large Cap | Equity Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8,520	9,212
U.S. Mid Cap | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,613	2,852
U.S. Mid Cap | Equity Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,613	2,852
U.S. Small Cap | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,649	2,626
U.S. Small Cap | Equity Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,649	2,626
International Developed | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,406	6,181
International Developed | Equity Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,406	6,181
Emerging Markets | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,114	4,139
Emerging Markets | Equity Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,114	4,139
Core Fixed Income | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,782	27,062
Core Fixed Income | Fixed Income Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,782	27,062
Long Duration Fixed Income | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,931	61,718
Long Duration Fixed Income | Fixed Income Securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55,931	61,718
REIT Fund | Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,212	2,395
REIT Fund | Real Estate | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,212	$ 2,395