Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 288,490	$ 266,592
Accounts receivable:
Trade, net of allowance for uncollectible accounts of $2,752	79,791	113,336
Unbilled and other	76,914	29,947
Other current assets	51,519	41,768
Total current assets	496,714	451,643
Property and equipment	2,722,845	2,695,772
Less accumulated depreciation	(938,538)	(889,783)
Property and equipment, net	1,784,307	1,805,989
Other assets, net	85,823	105,205
Total assets	2,366,844	2,362,837
Current liabilities:
Accounts payable	69,624	81,299
Accrued liabilities	81,087	71,680
Income tax payable	1,477	2,799
Current maturities of long-term debt	46,151	109,861
Total current liabilities	198,339	265,639
Long-term debt	412,852	385,766
Deferred tax liabilities	106,560	103,349
Other non-current liabilities	46,699	40,690
Total liabilities	764,450	795,444
Shareholders’ equity:
Common stock, no par, 240,000 shares authorized, 148,107 and 147,740 shares issued, respectively	1,303,984	1,284,274
Retained earnings	369,659	352,906
Accumulated other comprehensive loss	(71,249)	(69,787)
Total shareholders’ equity	1,602,394	1,567,393
Total liabilities and shareholders’ equity	$ 2,366,844	$ 2,362,837