Condensed Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Trade receivables, allowance for doubtful accounts	$ 8,045	$ 8,189
Common stock, par value (dollars per share)	$ 0	$ 0
Preferred Stock, 4 1/2% Cumulative
Preferred stock, par value (dollars per share)	$ 50	$ 50
Preferred Stock, Dividend Rate, Percentage	4.50%	4.50%