Qualified Employee Benefit Plans - Valuation of our Retirement Plan Assets by Pricing Observability Levels (Details) - Retirement Plan [Member] - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	$ 86,292	$ 90,320	$ 83,831
Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	67,189	71,138
Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	19,103	19,182
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	445	715
Cash [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	445	715
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
Hedge Fund [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	9,129	9,249
Hedge Fund [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Hedge Fund [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	9,129	9,249
Hedge Fund [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	21,555	22,040
Fixed Income Mutual Funds [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	21,555	22,040
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 Fund [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	21,660	23,220
Equity Mutual Fund [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	21,660	23,220
Equity Mutual Fund [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity Mutual Fund [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	23,529	25,163
Equity Securities [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	23,529	25,163
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
Equity Private Investment Trusts [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	9,974	9,933
Equity Private Investment Trusts [Member] | Level 1 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	0	0
Equity Private Investment Trusts [Member] | Level 2 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	9,974	9,933
Equity Private Investment Trusts [Member] | Level 3 [Member]
Defined Benefit Plan, Assets [Abstract]
Total assets measured at fair value	$ 0	$ 0