Employee Benefit Plans - Return on Current and Target Asset Allocation (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	$ 19,726		$ 18,367
Cash and other investments
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	886		716
Fixed income securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	3,896		3,328
Equity securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	14,944	[1]	14,323	[1]
Level 1
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	14,469		14,718
Level 1 | Cash and other investments
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	886		716
Level 1 | Fixed income securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	3,896		3,328
Level 1 | Equity securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	9,687	[1]	10,674	[1]
Level 2
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	5,257		3,649
Level 2 | Cash and other investments
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	0		0
Level 2 | Fixed income securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	0		0
Level 2 | Equity securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	5,257	[1]	3,649	[1]
Level 3
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	0		0
Level 3 | Cash and other investments
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	0		0
Level 3 | Fixed income securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	0		0
Level 3 | Equity securities
Schedule of Defined Benefit Plan Asset Allocation Targets [Line Items]
Pension plan assets	$ 0	[1]	$ 0	[1]

[1] Represents mutual funds and commingled accounts which invest primarily in equities, but may also hold fixed income securities, cash and other investments.