Employee Benefit Plans - Schedule of Categorization of Plans' Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 672,576	$ 643,844
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	13,226	5,835
Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	52,439	43,764
Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	31,253	27,762
Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	1,339	44,728
Debt Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	372,885	337,976
Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	201,434	183,779
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	305,843	273,989
Level 1 [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	13,226	5,835
Level 1 [Member] | Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	52,439	43,764
Level 1 [Member] | Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	31,253	27,762
Level 1 [Member] | Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	457	907
Level 1 [Member] | Debt Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	13,570	11,942
Level 1 [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	194,898	183,779
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	364,362	366,935
Level 2 [Member] | Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	304	43,123
Level 2 [Member] | Debt Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	357,522	323,812
Level 2 [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	6,536
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	2,371	2,920
Level 3 [Member] | Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	578	698
Level 3 [Member] | Debt Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 1,793	$ 2,222