Committed Lines of Credit (Tables)

12 Months Ended

Dec. 31, 2016

Short-term Debt [Abstract]

Schedule of Line of Credit Facilities [Table Text Block]

	2016			2015
Balance outstanding at end of period	$	120,000		$	105,000
Letters of credit outstanding at end of period	$	34,353		$	44,595
Average interest rate at end of period	1.50		%	1.18		%