Fair Value (Details) - Annual Fair Value Measurements of Pension Plan Asses - USD ($) $ in Thousands		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		$ 65,189	[1]	$ 64,903	$ 72,193
Mutual fund
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	29,071		23,061
U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		13,904		12,404
Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		7,010		9,569
Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		7,526		11,330
Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		7,678		8,539
Level 1
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		42,554		41,257
Level 1 | Mutual fund
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	29,071		23,061
Level 1 | U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		5,957		6,866
Level 1 | Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		0
Level 1 | Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		7,526		11,330
Level 1 | Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		0
Level 2
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		22,635		23,646
Level 2 | Mutual fund
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	0		0
Level 2 | U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		7,947		5,538
Level 2 | Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		7,010		9,569
Level 2 | Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		0		0
Level 2 | Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		$ 7,678		$ 8,539

[1] Additional information regarding the fair value of Pension Plan assets as of December 31, 2016 can be found in Note 22, "Fair Value."

[2] Includes mutual funds, money market funds, cash, cash equivalents, and accrued interest.