Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 273,985	$ 266,592
Accounts receivable:
Trade, net of allowance for uncollectible accounts of $2,752	77,956	113,336
Unbilled and other	43,353	29,947
Other current assets	46,236	41,768
Total current assets	441,530	451,643
Property and equipment	2,721,339	2,695,772
Less accumulated depreciation	(919,113)	(889,783)
Property and equipment, net	1,802,226	1,805,989
Other assets, net	95,392	105,205
Total assets	2,339,148	2,362,837
Current liabilities:
Accounts payable	71,722	81,299
Accrued liabilities	64,396	71,680
Income tax payable	0	2,799
Current maturities of long-term debt	46,492	109,861
Total current liabilities	182,610	265,639
Long-term debt	420,878	385,766
Deferred tax liabilities	108,546	103,349
Other non-current liabilities	38,096	40,690
Total liabilities	750,130	795,444
Commitments and contingencies
Shareholders’ equity:
Common stock, no par, 240,000 shares authorized, 148,080 and 147,740 shares issued, respectively	1,301,299	1,284,274
Retained earnings	351,876	352,906
Accumulated other comprehensive loss	(64,157)	(69,787)
Total shareholders’ equity	1,589,018	1,567,393
Total liabilities and shareholders’ equity	$ 2,339,148	$ 2,362,837