Employee Benefit and Deferred Compensation Plans (Details 5) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair values of defined benefit pension plan assets by category of the firm
Fair value	$ 26,913	$ 25,241
Cash and cash equivalents
Fair values of defined benefit pension plan assets by category of the firm
Fair value	387	1,639
U.S. government securities
Fair values of defined benefit pension plan assets by category of the firm
Fair value	2,496	2,270
Corporate debt
Fair values of defined benefit pension plan assets by category of the firm
Fair value	1,908	1,991
Corporate stocks
Fair values of defined benefit pension plan assets by category of the firm
Fair value	20,557	17,823
Investments in registered investment companies
Fair values of defined benefit pension plan assets by category of the firm
Fair value	921	871
Foreign obligations
Fair values of defined benefit pension plan assets by category of the firm
Fair value	644	647
Quoted Prices In Active Markets for Identical Assets (Level 1)
Fair values of defined benefit pension plan assets by category of the firm
Fair value	21,865	20,333
Quoted Prices In Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Fair values of defined benefit pension plan assets by category of the firm
Fair value	387	1,639
Quoted Prices In Active Markets for Identical Assets (Level 1) | U.S. government securities
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate debt
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Quoted Prices In Active Markets for Identical Assets (Level 1) | Corporate stocks
Fair values of defined benefit pension plan assets by category of the firm
Fair value	20,557	17,823
Quoted Prices In Active Markets for Identical Assets (Level 1) | Investments in registered investment companies
Fair values of defined benefit pension plan assets by category of the firm
Fair value	921	871
Quoted Prices In Active Markets for Identical Assets (Level 1) | Foreign obligations
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Other Observable Inputs (Level 2)
Fair values of defined benefit pension plan assets by category of the firm
Fair value	5,048	4,908
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Other Observable Inputs (Level 2) | U.S. government securities
Fair values of defined benefit pension plan assets by category of the firm
Fair value	2,496	2,270
Significant Other Observable Inputs (Level 2) | Corporate debt
Fair values of defined benefit pension plan assets by category of the firm
Fair value	1,908	1,991
Significant Other Observable Inputs (Level 2) | Corporate stocks
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Other Observable Inputs (Level 2) | Investments in registered investment companies
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Other Observable Inputs (Level 2) | Foreign obligations
Fair values of defined benefit pension plan assets by category of the firm
Fair value	644	647
Significant Unobservable Inputs (Level 3)
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Unobservable Inputs (Level 3) | U.S. government securities
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Unobservable Inputs (Level 3) | Corporate debt
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Unobservable Inputs (Level 3) | Corporate stocks
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Unobservable Inputs (Level 3) | Investments in registered investment companies
Fair values of defined benefit pension plan assets by category of the firm
Fair value	0	0
Significant Unobservable Inputs (Level 3) | Foreign obligations
Fair values of defined benefit pension plan assets by category of the firm
Fair value	$ 0	$ 0