Employee Benefit Plan - Major Categories of Assets in Pension Plan (Details) - DB Pension Plan - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	$ 80,154	$ 71,807	$ 68,931
(Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	80,154	71,057
(Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	750
(Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	0
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	448	1,147
Cash and cash equivalents | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	448	1,147
Cash and cash equivalents | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	0
Cash and cash equivalents | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	0
Common stocks
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	24,994	23,291
Common stocks | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	24,994	23,291
Common stocks | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	0
Common stocks | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	0
Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	54,712	46,619
Mutual funds | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	54,712	46,619
Mutual funds | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	0	0
Mutual funds | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets	$ 0	0
Preferred stocks
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets		750
Preferred stocks | (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets		0
Preferred stocks | (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets		750
Preferred stocks | (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total Fair Value of Plan Assets		$ 0