Annual report pursuant to Section 13 and 15(d)

Selected Quarterly Data (Unaudited) (Details)

v3.10.0.1
Selected Quarterly Data (Unaudited) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Dec. 31, 2018
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Dec. 31, 2017
Sep. 30, 2017
Jun. 30, 2017
Mar. 31, 2017
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Quarterly Financial Data [Abstract]                      
Revenues $ 180,996 $ 168,931 $ 170,394 $ 176,897 $ 194,795 $ 174,164 $ 193,860 $ 197,294 $ 697,218 $ 760,113 $ 691,790
Costs and operating expenses 167,911 154,934 156,539 165,304 181,908 161,927 178,855 183,098 644,688 705,788 640,261
Operating income 13,085 15,697 13,855 11,593 12,887 12,237 15,005 14,196 54,230 54,325 51,529
Net income $ 9,243 10,034 $ 8,751 $ 7,052 $ 17,357 $ 6,639 $ 7,807 $ 7,293 35,080 39,096 26,793
Gain on sale of contract   $ 1,700             $ 1,700 $ 0 $ 0
Basic earnings per share:                      
Net income (in dollars per share) $ 0.85 $ 0.92 $ 0.80 $ 0.65 $ 1.60 $ 0.61 $ 0.72 $ 0.67 $ 3.23 $ 3.61 $ 2.48
Basic weighted average shares outstanding (in shares) 10,882,000 10,881,000 10,881,000 10,861,000 10,838,000 10,838,000 10,838,000 10,823,000 10,876,201 10,834,562 10,793,723
Diluted earnings per share:                      
Net income (in dollars per share) $ 0.84 $ 0.92 $ 0.80 $ 0.65 $ 1.59 $ 0.61 $ 0.72 $ 0.67 $ 3.21 $ 3.60 $ 2.47
Diluted weighted average shares outstanding (in shares) 10,993,000 10,935,000 10,919,000 10,897,000 10,903,000 10,857,000 10,862,000 10,849,000 10,936,057 10,867,834 10,828,152