Fair Value of Financial Instruments (Details 4) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Total
Pension Plan Assets
Fair values of plan assets	$ 193,429	$ 176,693
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	193,429	176,693
Total | Growth funds
Pension Plan Assets
Fair values of plan assets	49,408	44,879
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	49,408	44,879
Total | Income funds
Pension Plan Assets
Fair values of plan assets	23,925	28,473
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	23,925	28,473
Total | Growth and income funds
Pension Plan Assets
Fair values of plan assets	83,759	73,186
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	83,759	73,186
Total | Hedge funds
Pension Plan Assets
Fair values of plan assets	25,624	22,615
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	25,624	22,615
Total | Real estate funds
Pension Plan Assets
Fair values of plan assets	3,279	3,300
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	3,279	3,300
Total | Other assets
Pension Plan Assets
Fair values of plan assets	1,040	2,199
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	1,040	2,199
Total | Cash and cash equivalents
Pension Plan Assets
Fair values of plan assets	6,394	2,041
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	6,394	2,041
Level 1
Pension Plan Assets
Fair values of plan assets	81,052	74,880
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	81,052	74,880
Level 1 | Growth funds
Pension Plan Assets
Fair values of plan assets	49,408	43,616
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	49,408	43,616
Level 1 | Income funds
Pension Plan Assets
Fair values of plan assets	23,925	27,428
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	23,925	27,428
Level 1 | Real estate funds
Pension Plan Assets
Fair values of plan assets	731	714
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	731	714
Level 1 | Other assets
Pension Plan Assets
Fair values of plan assets	594	1,081
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	594	1,081
Level 1 | Cash and cash equivalents
Pension Plan Assets
Fair values of plan assets	6,394	2,041
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	6,394	2,041
Level 2
Pension Plan Assets
Fair values of plan assets	86,753	79,198
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	86,753	79,198
Level 2 | Growth funds
Pension Plan Assets
Fair values of plan assets		1,263
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period		1,263
Level 2 | Income funds
Pension Plan Assets
Fair values of plan assets		1,045
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period		1,045
Level 2 | Growth and income funds
Pension Plan Assets
Fair values of plan assets	83,759	73,186
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	83,759	73,186
Level 2 | Real estate funds
Pension Plan Assets
Fair values of plan assets	2,548	2,586
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	2,548	2,586
Level 2 | Other assets
Pension Plan Assets
Fair values of plan assets	446	1,118
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	446	1,118
Level 3
Pension Plan Assets
Fair values of plan assets	25,624	22,615
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at beginning of period	22,615	22,523
Unrealized gain (loss)	3,067	930
Realized gain (loss)	13	448
Purchases		3,000
Sales/settlements	(71)	(4,286)
Fair value of plan assets at end of period	25,624	22,615
Level 3 | Hedge funds
Pension Plan Assets
Fair values of plan assets	25,624	22,615
Summary of the changes in the fair value of the defined benefit plans assets classified within Level 3 of the valuation hierarchy
Fair value of plan assets at end of period	$ 25,624	$ 22,615