Benefit Plans - Assets Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Total investments	$ 41,448	$ 42,744
Group Annuity Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	134	152
Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	18,848	8,368
Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	22,466	34,224
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	18,848	8,368
Level 1 [Member] | Group Annuity Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	18,848	8,368
Level 1 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	22,600	34,376
Level 2 [Member] | Group Annuity Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	134	152
Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Level 2 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	22,466	34,224
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Level 3 [Member] | Group Annuity Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Level 3 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Fixed Income [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments		0
Fixed Income [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	8,653	19,789
Fixed Income [Member] | Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments		0
Fixed Income [Member] | Level 1 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Fixed Income [Member] | Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments		0
Fixed Income [Member] | Level 2 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	8,653	19,789
Fixed Income [Member] | Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments		0
Fixed Income [Member] | Level 3 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
International Equity [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	4,455	5,370
International Equity [Member] | Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	4,455	5,370
International Equity [Member] | Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
International Equity [Member] | Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Large U S Equity [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	1,224	1,689
Large U S Equity [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	10,962	11,857
Large U S Equity [Member] | Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	1,224	1,689
Large U S Equity [Member] | Level 1 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Large U S Equity [Member] | Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Large U S Equity [Member] | Level 2 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	10,962	11,857
Large U S Equity [Member] | Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Large U S Equity [Member] | Level 3 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Small Mid U S Equity [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	791	1,309
Small Mid U S Equity [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	2,851	2,578
Small Mid U S Equity [Member] | Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	791	1,309
Small Mid U S Equity [Member] | Level 1 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Small Mid U S Equity [Member] | Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Small Mid U S Equity [Member] | Level 2 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	2,851	2,578
Small Mid U S Equity [Member] | Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	0
Small Mid U S Equity [Member] | Level 3 [Member] | Pooled Separate Accounts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0	$ 0
Fixed Income [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	12,378
Fixed Income [Member] | Level 1 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	12,378
Fixed Income [Member] | Level 2 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	0
Fixed Income [Member] | Level 3 [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total investments	$ 0