Employee Benefit Plans - Fair Value of Plan Assets (Detail) - Pension Benefits [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 1,965,502	$ 1,912,736	$ 2,021,837
Assets Measured at NAV	196,576	190,682
Common Stocks - Mutual Funds - Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	384,103	349,852
Assets Measured at NAV	114,182	107,441
Genuine Parts Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	192,841	173,363
Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	793,101	793,229
Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	55,607	46,195
Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	15,995	2,978
Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	157,303	193,436
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	192,457	172,119
Asset Backed and Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	8,872	27,510
Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	216	434
Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	24,613	21,137
Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	9,272	5,857
Municipal Funds-Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	128,367	123,895
Assets Measured at NAV	82,394	83,241
Cash Surrender Value of Life Insurance Policies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,755	2,731
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1,450,707	1,387,915
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Common Stocks - Mutual Funds - Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	269,921	242,411
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Genuine Parts Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	192,841	173,363
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	793,007	792,624
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	55,607	46,195
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	15,995	2,978
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	102,468	109,559
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Asset Backed and Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	20,868	20,785
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Municipal Funds-Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash Surrender Value of Life Insurance Policies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	315,370	330,803
Significant Observable Inputs (Level 2) [Member] | Common Stocks - Mutual Funds - Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Genuine Parts Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Observable Inputs (Level 2) [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	54,835	83,877
Significant Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	192,457	172,119
Significant Observable Inputs (Level 2) [Member] | Asset Backed and Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	8,872	27,510
Significant Observable Inputs (Level 2) [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	216	434
Significant Observable Inputs (Level 2) [Member] | Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	3,745	352
Significant Observable Inputs (Level 2) [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	9,272	5,857
Significant Observable Inputs (Level 2) [Member] | Municipal Funds-Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	45,973	40,654
Significant Observable Inputs (Level 2) [Member] | Cash Surrender Value of Life Insurance Policies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,849	3,336
Significant Unobservable Inputs (Level 3) [Member] | Common Stocks - Mutual Funds - Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Genuine Parts Company [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	94	605
Significant Unobservable Inputs (Level 3) [Member] | Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Asset Backed and Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Municipal Funds-Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	0	0
Significant Unobservable Inputs (Level 3) [Member] | Cash Surrender Value of Life Insurance Policies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 2,755	$ 2,731