CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 81,591	$ 74,712
Trade receivables, net	18,887	16,781
Inventories, net	11,346	12,433
Prepaid expenses and other current assets	1,180	1,110
Total current assets	113,004	105,036
Property, plant and equipment	292,553	285,594
Less accumulated depreciation and depletion	(186,193)	(180,613)
Property, plant and equipment, net	106,360	104,981
Other assets, net	145	142
Total assets	219,509	210,159
Current liabilities:
Accounts payable	5,616	5,587
Accrued expenses	4,541	3,521
Total current liabilities	10,157	9,108
Deferred tax liabilities, net	18,998	19,832
Other liabilities	1,511	1,580
Total liabilities	30,666	30,520
Stockholders' equity:
Common stock	657	657
Additional paid-in capital	23,557	22,831
Accumulated other comprehensive income (loss)	56	(223)
Retained earnings	218,162	209,770
Less treasury stock, at cost	(53,589)	(53,396)
Total stockholders' equity	188,843	179,639
Total liabilities and stockholders' equity	$ 219,509	$ 210,159

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Name:	us-gaap_AccountsPayableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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.