Nature of Operations and Summary of Significant Accounting Policies (Details 9) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares shares	Mar. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) segment $ / shares shares	Dec. 31, 2014 USD ($) $ / shares shares	Dec. 31, 2013 USD ($) $ / shares shares
Net Income (loss) Per Common Share
Number of outstanding options not included in computation of Diluted EPS (in shares) | shares									505,000	3,191,000	3,072,000
Numerator
Net Income (loss)	$ 40,454	$ 36,268	$ 31,475	$ 9,620	$ (27,868)	$ 41,338	$ (14,737)	$ (22,887)	$ 117,817	$ (24,154)	$ 58,956
Denominator
Denominator for basic earnings per-share weighted average shares | shares	50,880,000	50,616,000	51,357,000	51,457,000	51,174,000	51,127,000	51,183,000	51,467,000	51,077,000	51,237,000	51,688,000
Dilution due to stock options and restricted stock (in shares) | shares									748,000		734,000
Denominator for diluted earnings per-share weighted average shares | shares	51,657,000	51,282,000	51,971,000	52,392,000	51,174,000	52,036,000	51,183,000	51,467,000	51,825,000	51,237,000	52,422,000
Basic earnings per share (in dollars per share) | $ / shares	$ 0.80	$ 0.72	$ 0.61	$ 0.19	$ (0.54)	$ 0.81	$ (0.29)	$ (0.44)	$ 2.31	$ (0.47)	$ 1.14
Diluted earnings per share (in dollars per share) | $ / shares	$ 0.78	$ 0.71	$ 0.61	$ 0.18	$ (0.54)	$ 0.79	$ (0.29)	$ (0.44)	$ 2.27	$ (0.47)	$ 1.12
Other Revenue Items
Deemed rental income under code-share agreement									$ 504,900	$ 497,000	$ 500,200
Fair Value of Financial Instruments
Fair value of long-term debt	$ 1,939,800				$ 1,813,100				1,939,800	1,813,100
Carrying amount of long-term debt	1,948,803				$ 1,745,811				$ 1,948,803	$ 1,745,811
Segment Reporting
Operating segments number | segment									3
Recent Accounting Pronouncements
Unamortized debt issuance costs	$ 20,900								$ 20,900
Previously reported
Prior Period Adjustment [Abstract]
Overstatement of prepaid expense									201,500
Understatement of long term prepaid aircraft									$ 201,500