Fair Value - Annual Fair Value Measurements of Pension Plan Asses (Details) - USD ($) $ in Thousands		Dec. 31, 2018		Dec. 31, 2017	Dec. 31, 2016
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		$ 76,210	[1]	$ 66,159	$ 65,189
Mutual funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	27,246		41,002
U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		8,015		13,075
Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		10,472		9,171
Common stocks
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		26,882		0
Common trust funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		3,595		2,911
Level 1
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		58,517		44,680
Level 1 | Mutual funds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets	[2]	27,246		41,002
Level 1 | U.S. agency securities
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		4,389		3,678
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		26,882		0
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		17,693		21,479
Level 2 | Mutual funds
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		3,626		9,397
Level 2 | Corporate bonds
Fair Value Defined Benefit Plan Disclosure [Line Items]
Pension plan assets		10,472		9,171
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		$ 3,595		$ 2,911

[1] Additional information regarding the fair value of Pension Plan assets as of December 31, 2018 can be found in Note 21, "Fair Value."

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