Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Current assets
Cash and cash equivalents	$ 206,692	$ 102,335	$ 65,302
Accounts receivable—trade, less allowance for doubtful accounts of $1,988 in 2016 and $1,963 in 2015	139,692	136,253
Inventories, at lower of cost or market	152,542	155,906
Prepaid expenses and other current assets	29,153	41,173
Total current assets	528,079	435,667
Property, plant and equipment, at cost less accumulated depreciation and amortization of $756,305 in 2016 and $724,486 in 2015	1,488,261	1,369,318
Restricted cash	0	68,571
Other assets	40,489	12,685
Total assets	2,056,829	1,886,241
Current liabilities
Current maturities of long-term debt	40,471	222
Trade accounts payable and accrued liabilities	376,897	390,341
Deferred income taxes	0	1,729
Total current liabilities	417,368	392,292
Long-term debt, including capitalized lease obligations	638,911	490,160
Deferred income taxes	200,601	161,236
Asset retirement obligations	25,637	24,345
Deferred credits and other liabilities	15,125	25,918
Total liabilities	1,297,642	1,093,951
Stockholders' Equity
Preferred Stock, par $0.01, (authorized 20,000,000 shares, none outstanding)	0	0
Common Stock, par $0.01, (authorized 200,000,000 shares, 46,767,164 and 46,767,164 shares issued at 2016 and 2015, respectively)	468	468
Treasury stock (8,167,623 and 5,088,434 shares held at September 30, 2016 and December 31, 2015, respectively)	(497,111)	(294,139)
Additional paid in capital (APIC)	550,376	558,182
Retained earnings	705,454	527,779
Total stockholders' equity	759,187	792,290	$ 723,440	$ 858,705
Total liabilities and stockholders' equity	$ 2,056,829	$ 1,886,241

Sum of the carrying values as of the balance sheet date of obligations incurred through that date and due within one year (or the operating cycle, if longer), including liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received, taxes, interest, rent and utilities, accrued salaries and bonuses, payroll taxes and fringe benefits.

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Period Type:	instant

- Definition

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.