Quarterly Results of Operations (Tables)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

A summary of quarterly results of operations for the years ended December 31, 2015 and 2014 follows.

	QUARTER ENDED
	DEC. 31,		SEPT. 30,		JUNE 30,		MAR. 31,		DEC. 31,		SEPT. 30,		JUNE 30,		MAR. 31,
	2015		2015		2015		2015		2014		2014		2014		2014
Operating revenue	$	199,382	$	198,972	$	203,518	$	206,901	$	203,685	$	198,356	$	192,960	$	197,630
Income from continuing operations	82,363		93,695		36,526		31,862		84,193		35,318		29,811		26,260
Discontinued operations	—		—		—		—		306		133		296		47,846
Net income	82,363		93,695		36,526		31,862		84,499		35,451		30,107		74,106
Income per common share - basic (1)	0.55		0.61		0.24		0.21		0.56		0.23		0.20		0.49
Income per common share - diluted (1)	0.55		0.61		0.24		0.21		0.55		0.23		0.20		0.49

(1) The sum of quarterly financial data may vary from the annual data due to rounding.