Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 322,357	$ 384,567
Accounts receivable, net	280,019	212,586
Inventories, net	167,415	92,376
Prepaid expenses and other current assets	14,439	13,715
Income tax deposits	3,191	0
Total current assets	787,421	703,244
Property, plant and mine development, net	1,825,653	1,169,155
Goodwill	414,257	272,079
Intangible assets, net	194,795	150,007
Other assets	27,219	12,798
Total assets	3,249,345	2,307,283
Current Liabilities:
Accounts payable and accrued expenses	206,994	171,041
Current portion of long-term debt	13,969	6,867
Current portion of deferred revenue	52,021	36,128
Income tax payable	0	1,566
Total current liabilities	272,984	215,602
Long-term debt, net	1,253,384	505,075
Deferred revenue	59,424	82,286
Liability for pension and other post-retirement benefits	47,022	52,867
Deferred income taxes, net	172,610	29,856
Other long-term obligations	85,417	25,091
Total liabilities	1,890,841	910,777
Commitments and Contingencies (Note O)
Stockholders’ Equity:
Preferred stock, $0.01 par value, 10,000,000 shares authorized; zero issued and outstanding at June 30, 2018 and December 31, 2017	0	0
Common stock, $0.01 par value, 500,000,000 shares authorized; 81,734,599 issued and 77,681,643 outstanding at June 30, 2018; 81,267,205 issued and 80,524,255 outstanding at December 31, 2017	815	812
Additional paid-in capital	1,160,235	1,147,084
Retained earnings	327,173	287,992
Treasury stock, at cost, 4,052,956 and 742,950 shares at June 30, 2018 and December 31, 2017, respectively	(120,056)	(25,456)
Accumulated other comprehensive loss	(9,663)	(13,926)
Total stockholders’ equity	1,358,504	1,396,506
Total liabilities and stockholders’ equity	$ 3,249,345	$ 2,307,283