Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current Assets:
Cash and cash equivalents	$ 598,535	$ 711,225
Accounts receivable, net	159,110	89,006
Inventories, net	74,278	78,709
Prepaid expenses and other current assets	10,254	12,323
Income tax deposits	0	1,682
Total current assets	842,177	892,945
Property, plant and mine development, net	919,840	783,313
Goodwill	246,181	240,975
Trade names	33,068	32,318
Intellectual property, net	65,384	57,270
Customer relationships, net	52,508	50,890
Other assets	15,013	15,509
Total assets	2,174,171	2,073,220
Current Liabilities:
Accounts payable	102,376	70,778
Dividends payable	5,229	5,221
Accrued liabilities	14,698	13,034
Accrued interest	61	169
Current portion of long-term debt	4,832	4,821
Current portion of capital leases	1,961	2,237
Current portion of deferred revenue	25,402	13,700
Income tax payable	2,791	0
Total current liabilities	157,350	109,960
Long-term debt	506,295	508,417
Deferred revenue	79,808	58,090
Obligations under capital lease	138	717
Liability for pension and other post-retirement benefits	59,411	56,746
Deferred income taxes, net	52,328	50,075
Other long-term obligations	16,633	15,925
Total liabilities	871,963	799,930
Stockholders’ Equity:
Preferred stock	0	0
Common stock	812	811
Additional paid-in capital	1,134,245	1,129,051
Retained earnings	184,959	163,173
Treasury stock, at cost	(491)	(3,869)
Accumulated other comprehensive loss	(17,317)	(15,876)
Total stockholders’ equity	1,302,208	1,273,290
Total liabilities and stockholders’ equity	$ 2,174,171	$ 2,073,220