Quarterly Results of Operations (unaudited) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of quarterly results of operations (unaudited)

	Year ended December 31, 2017
(in thousands, except per share data)	First quarter		Second quarter		Third quarter		Fourth quarter		Year
Operating revenue	$	399,316	$	448,564	$	442,492	$	401,402	$	1,691,774
Operating expenses	332,782		365,520		361,656		343,444		1,403,402
Investment income	6,586		6,448		8,406		7,121		28,561
Interest expense, net	166		257		377		438		1,238
Income before income taxes	72,954		89,235		88,865		64,641		315,695
Net income	$	47,876	$	58,527	$	58,543	$	32,053	$	196,999
Earnings per share (1)
Net income per share
Class A common stock – basic	$	1.03	$	1.26	$	1.26	$	0.69	$	4.23
Class A common stock – diluted (2)	$	0.91	$	1.12	$	1.12	$	0.61	$	3.76
Class B common stock – basic	$	154	$	189	$	189	$	103	$	635
Class B common stock – diluted	$	154	$	188	$	189	$	103	$	634

(1) The cumulative sum of quarterly basic and diluted net income per share amounts may not equal total basic and diluted net income per share for the year due to differences in weighted average shares and equivalent shares outstanding for each of the periods presented.

(2) Class A diluted earnings per share was reduced by $0.19 for the fourth quarter and total year as a result of increased income tax expense from enactment of the TCJA of $10.1 million. See Note 3, "Earnings Per Share" and Note 10, "Income Taxes".

	Year ended December 31, 2016
(in thousands, except per share data)	First quarter		Second   quarter		Third  quarter		Fourth  quarter		Year
Operating revenue	$	374,728	$	423,884	$	418,406	$	379,613	$	1,596,631
Operating expenses	307,063		338,125		336,151		322,928		1,304,267
Investment income	2,559		7,404		4,326		13,539		27,828
Interest expense, net	—		—		—		101		101
Income before income taxes	70,224		93,163		86,581		70,123		320,091
Net income	$	45,895	$	61,309	$	57,376	$	45,786	$	210,366
Earnings per share (1)
Net income per share
Class A common stock – basic	$	0.99	$	1.32	$	1.23	$	0.98	$	4.52
Class A common stock –diluted	$	0.87	$	1.17	$	1.09	$	0.87	$	4.01
Class B common stock – basic	$	148	$	197	$	185	$	147	$	678
Class B common stock – diluted	$	148	$	197	$	185	$	147	$	677

(1) The cumulative sum of quarterly basic and diluted net income per share amounts may not equal total basic and diluted net income per share for the year due to differences in weighted average shares and equivalent shares outstanding for each of the periods presented.