Employee Benefit Plans - Defined Benefit Plan Assets at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 60,725	$ 55,631
U.S. Equity Securities Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,243	18,222
Non-U.S. Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,377	19,563
Fixed Income Securities Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,012	15,135
Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,762	2,609
Plan Assets, Subtotal [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60,394	55,529
Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	331	102
Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	57,963	53,022
Level 1 [Member] | U.S. Equity Securities Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18,243	18,222
Level 1 [Member] | Non-U.S. Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,377	19,563
Level 1 [Member] | Fixed Income Securities Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14,012	15,135
Level 1 [Member] | Plan Assets, Subtotal [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	57,632	52,920
Level 1 [Member] | Cash [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	331	102
Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,762	2,609
Level 2 [Member] | Alternative Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,762	2,609
Level 2 [Member] | Plan Assets, Subtotal [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,762	$ 2,609