Employee Benefit Plans - Schedule of Categorization of Plans' Assets (Detail) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		$ 646,119	$ 656,084
Fair Value of Plan Assets excluding the fair value of plan liabilities			656,668
Plan liabilities measured at Fair Value			584
Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan liabilities measured at Fair Value			584
Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		618
NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	[1]	349,751	332,084
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		295,750	324,584
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		618
Plan liabilities measured at Fair Value			584
Level 2 [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan liabilities measured at Fair Value			584
Level 2 [Member] | Derivative [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		618
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		23,341	19,172
Cash [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		23,341	19,172
Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		63,431	56,247
Debt [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		63,431	56,247
Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		29,287	25,901
Equities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		29,287	25,901
Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		24,278	1,193
Alternative Investment Funds [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	[1]	23,062	525
Alternative Investment Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		1,216	668
Debt Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		331,054	337,011
Debt Funds [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	[1]	320,560	325,312
Debt Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		10,494	11,699
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		174,110	217,144
Equity Funds [Member] | NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	[1]	6,129	6,247
Equity Funds [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value		$ 167,981	$ 210,897

[1] Represents certain investments measured at NAV or its equivalent as a practical expedient in determining fair value. In accordance with current accounting guidance, these investments have not been classified in the fair value hierarchy. See Note 3 for additional information.