Investments (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Investments at fair value	$ 2,528	$ 2,064
Unrealized losses			132
Unrealized gains	391	191
Losses on sale of investments	1		27
Gain on sale of investments		66
Investments [Line Items]
Cost method investments	4,109	3,724
Equity method investments	2,695	2,426
Total other investments	6,804	6,150
Increase in cost method investments	375	221
Distributions from equity investments	121
Change in value of equity method investment	364
Burton Partnership [Member]
Investments [Line Items]
Equity method investments	2,365	2,086
Change in value of equity method investment	279
Other [Member]
Investments [Line Items]
Equity method investments	330	340
Disposal of other investment	36
CoBank [Member]
Investments [Line Items]
Cost method investments	3,343	2,968
Other [Member]
Investments [Line Items]
Cost method investments	766	756
Taxable Bond Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments at fair value	10	728
Domestic equity funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments at fair value	2,419	1,265
International Equity Funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments at fair value	$ 99	$ 71