Annual report pursuant to Section 13 and 15(d)

Quarterly Results of Operations (Unaudited) (Details)

v2.4.1.9
Quarterly Results of Operations (Unaudited) (Details) (USD $)
In Thousands, except Per Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Quarterly Results of Operations (Unaudited) [Abstract]                      
Operating revenue $ 214,061us-gaap_Revenues $ 201,477us-gaap_Revenues $ 193,852us-gaap_Revenues $ 171,569us-gaap_Revenues $ 181,084us-gaap_Revenues $ 170,033us-gaap_Revenues $ 159,804us-gaap_Revenues $ 141,560us-gaap_Revenues $ 780,959us-gaap_Revenues $ 652,481us-gaap_Revenues $ 584,446us-gaap_Revenues
Income from operations 25,634us-gaap_OperatingIncomeLoss 26,906us-gaap_OperatingIncomeLoss 27,595us-gaap_OperatingIncomeLoss 16,271us-gaap_OperatingIncomeLoss 23,203us-gaap_OperatingIncomeLoss 22,857us-gaap_OperatingIncomeLoss 22,505us-gaap_OperatingIncomeLoss 15,790us-gaap_OperatingIncomeLoss 96,406us-gaap_OperatingIncomeLoss 84,355us-gaap_OperatingIncomeLoss 83,532us-gaap_OperatingIncomeLoss
Net income $ 17,045us-gaap_NetIncomeLoss $ 16,744us-gaap_NetIncomeLoss $ 17,178us-gaap_NetIncomeLoss $ 10,202us-gaap_NetIncomeLoss $ 15,584us-gaap_NetIncomeLoss $ 14,197us-gaap_NetIncomeLoss $ 13,831us-gaap_NetIncomeLoss $ 10,855us-gaap_NetIncomeLoss $ 61,169us-gaap_NetIncomeLoss $ 54,467us-gaap_NetIncomeLoss $ 52,668us-gaap_NetIncomeLoss
Net income per share:                      
Basic $ 0.56us-gaap_EarningsPerShareBasic $ 0.55us-gaap_EarningsPerShareBasic $ 0.56us-gaap_EarningsPerShareBasic $ 0.33us-gaap_EarningsPerShareBasic $ 0.51us-gaap_EarningsPerShareBasic $ 0.47us-gaap_EarningsPerShareBasic $ 0.46us-gaap_EarningsPerShareBasic $ 0.37us-gaap_EarningsPerShareBasic $ 1.99us-gaap_EarningsPerShareBasic $ 1.81us-gaap_EarningsPerShareBasic $ 1.82us-gaap_EarningsPerShareBasic
Diluted $ 0.55us-gaap_EarningsPerShareDiluted $ 0.54us-gaap_EarningsPerShareDiluted $ 0.55us-gaap_EarningsPerShareDiluted $ 0.33us-gaap_EarningsPerShareDiluted $ 0.50us-gaap_EarningsPerShareDiluted $ 0.46us-gaap_EarningsPerShareDiluted $ 0.45us-gaap_EarningsPerShareDiluted $ 0.36us-gaap_EarningsPerShareDiluted $ 1.96us-gaap_EarningsPerShareDiluted $ 1.77us-gaap_EarningsPerShareDiluted $ 1.78us-gaap_EarningsPerShareDiluted