Qualified Employee Benefit Plans - Valuation of our Retirement Plan Assets by Pricing Observability Levels (Details) - Retirement Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Assets [Abstract]
Total assets in the fair value hierarchy excluding net asset value investments	$ 67,512	$ 67,189
Investments measured at net assets value	19,187	19,103
Total assets measured at fair value	86,699	86,292	$ 90,320
Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	67,512	67,189
Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Level 3 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Cash [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	344	445
Cash [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	344	445
Cash [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Cash [Member] | Level 3 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Fixed Income Mutual Funds [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	21,441	21,555
Fixed Income Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	21,441	21,555
Fixed Income Mutual Funds [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Fixed Income Mutual Funds [Member] | Level 3 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity Mutual Funds [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	25,037	23,603
Equity Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	25,037	23,603
Equity Mutual Funds [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity Mutual Funds [Member] | Level 3 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity Securities [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	20,690	21,586
Equity Securities [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	20,690	21,586
Equity Securities [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity Securities [Member] | Level 3 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	$ 0	$ 0