Employee Benefit Plans - Fair Value of Plan Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 1,912,736	$ 2,021,837
Common Stocks - Mutual Funds - Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	349,852	366,716
Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	793,229	822,782
Short-Term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	46,195	41,882
Cash and Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,978	8,921
Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	193,436	192,413
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	172,119	178,214
Asset Backed and Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	27,510	27,756
Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	434	633
Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	21,137	25,137
Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	5,857	6,435
Mutual Funds - Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	123,895	132,752
Options and Futures [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		7
Cash Surrender Value of Life Insurance Policies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	2,731	2,712
Genuine Parts Company Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	173,363	215,477
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	1,495,356	1,574,080
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	349,852	366,716
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	792,624	822,782
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	46,195	41,882
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	2,978	8,921
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	109,559	96,480
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	20,785	21,815
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Options and Futures [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets		7
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Genuine Parts Company Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	173,363	215,477
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	414,044	445,045
Significant Observable Inputs (Level 2) [Member] | Government Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	83,877	95,933
Significant Observable Inputs (Level 2) [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	172,119	178,214
Significant Observable Inputs (Level 2) [Member] | Asset Backed and Mortgage Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	27,510	27,756
Significant Observable Inputs (Level 2) [Member] | Convertible Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	434	633
Significant Observable Inputs (Level 2) [Member] | Other-International [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	352	3,322
Significant Observable Inputs (Level 2) [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	5,857	6,435
Significant Observable Inputs (Level 2) [Member] | Mutual Funds - Fixed Income [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	123,895	132,752
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	3,336	2,712
Significant Unobservable Inputs (Level 3) [Member] | Other Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	605
Significant Unobservable Inputs (Level 3) [Member] | Cash Surrender Value of Life Insurance Policies [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of assets	$ 2,731	$ 2,712