Condensed Consolidated Statements of Cash Flows (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Cash flows from operating activities:    
Net cash provided by operating activities $ 51,531 $ 42,465
Cash flows from investing activities:    
Capital expenditures (50,053) (58,519)
Purchases of marketable securities (36,650) (10,123)
Sales and maturities of marketable securities 27,240 15,981
Net cash used in investing activities (59,463) (52,661)
Cash flows from financing activities:    
Borrowings under the Credit Facility 22,368 25,284
Payment of deferred financing fees (1,649) (1,828)
Restricted cash deposits (2,477) (13,350)
Proceeds from exercise of stock options 340 2
Tax payment upon settlement of stock awards (680) (20)
Excess tax benefits from stock-based compensation 533 0
Net cash provided by financing activities 14,576 8,338
Effect of exchange rate changes on cash and cash equivalents (115) 0
Net increase (decrease) in cash and cash equivalents 6,529 (1,858)
Cash and cash equivalents, beginning of period 211,249 186,342
Cash and cash equivalents, end of period 217,778 184,484
Supplemental cash flow information:    
Income taxes paid 426 229
Supplemental disclosure of non-cash investing activities:    
Property and equipment received but not paid for yet 1,314 3,915
Interest capitalized but not paid 24,544 20,047
Capitalized amortization of deferred financing costs 4,422 3,508
Capitalized stock-based compensation 302 293
Series Preferred Stock [Member]    
Cash flows from financing activities:    
Payment of preferred stock dividends (1,750) (1,750)
Supplemental disclosure of non-cash financing activities:    
Dividends Payable 292 292
Series B Preferred Stock [Member]    
Cash flows from financing activities:    
Payment of preferred stock dividends (2,109) 0
Supplemental disclosure of non-cash financing activities:    
Dividends Payable $ 351 $ 0