Condensed Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2015
Trade receivables, allowance for doubtful accounts	$ 7,525	$ 8,189
Common stock, par value (dollars per share)	$ 0	$ 0
Preferred Stock, 4 1/2% Cumulative
Preferred stock, dividend rate (percentage)	4.50%	4.50%
Preferred stock, par value (dollars per share)	$ 50	$ 50