Condensed Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Statement of Cash Flows [Abstract]
Net cash provided by Operating Activities	$ 252,163	$ 207,475
Cash flows from Investing Activities:
Additions to property and equipment, including pre-delivery payments, net	(361,290)	(232,717)
Net proceeds from disposition of equipment	978	0
Purchases of investments	(346,010)	0
Sales of investments	92,103	0
Net cash used in investing activities	(614,219)	(232,717)
Cash flows from Financing Activities:
Proceeds from exercise of stock options	5,487	2,376
Long-term borrowings	293,430	132,000
Repayments of long-term debt and capital lease obligations	(46,392)	(45,200)
Debt issuance costs	(32)	(12,416)
Change in restricted cash	14,434	(16,000)
Net cash provided by financing activities	266,927	60,760
Net increase (decrease) in cash and cash equivalents	(95,129)	35,518
Cash and cash equivalents - Beginning of Period	423,384	405,880
Cash and cash equivalents - End of Period	$ 328,255	$ 441,398