CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 68,940	$ 59,926
Trade receivables, net	19,385	15,889
Inventories, net	12,713	14,728
Prepaid expenses and other current assets	718	1,418
Total current assets	101,756	91,961
Property, plant and equipment	281,391	271,686
Less accumulated depreciation and depletion	(177,961)	(167,308)
Property, plant and equipment, net	103,430	104,378
Other assets, net	144	160
Total assets	205,330	196,499
Current liabilities:
Accounts payable	4,216	6,022
Accrued expenses	3,276	2,720
Total current liabilities	7,492	8,742
Deferred tax liabilities, net	19,495	19,184
Other liabilities	1,856	1,946
Total liabilities	28,843	29,872
Stockholders' equity:
Common stock	656	655
Additional paid-in capital	22,572	21,642
Retained earnings	206,545	194,798
Less treasury stock, at cost	(53,286)	(50,468)
Total stockholders' equity	176,487	166,627
Total liabilities and stockholders' equity	$ 205,330	$ 196,499

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.