Employee Benefits - Pension Plan Assets Measured at Fair Value on Recurring Basis (Details) - Fair Value Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	$ 87,613	$ 84,585
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	3,336	3,371
Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	27,279	27,054
Equity Index Mutual Funds-International
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	3,362	3,421
Domestic Individual Equities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	53,636	50,739
Level 1
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	84,277	81,214
Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 1 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	27,279	27,054
Level 1 | Equity Index Mutual Funds-International
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	3,362	3,421
Level 1 | Domestic Individual Equities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	53,636	50,739
Level 2
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	3,336	3,371
Level 2 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	3,336	3,371
Level 2 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 2 | Equity Index Mutual Funds-International
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 2 | Domestic Individual Equities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 3 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 3 | Fixed Income
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 3 | Equity Index Mutual Funds-International
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	0	0
Level 3 | Domestic Individual Equities
Defined Benefit Plan Disclosure [Line Items]
Pension plan assets measured at fair value	$ 0	$ 0