RESTRICTED INVESTMENTS AND BOND COLLATERAL (Tables)

12 Months Ended

Dec. 31, 2012

Disclosure Restricted Investments and Bond Collateral [Abstract]

Components of restricted investments and bond collateral

The Company’s restricted investments and bond collateral consist of the following:

	December 31,
	2012		2011
	(In thousands)
Coal Segment:
WML debt reserve account	$	13,062	$	11,664
Reclamation bond collateral:
Kemmerer Mine	24,702		—
Absaloka Mine	14,507		13,593
Rosebud Mine	12,495		12,264
Beulah Mine	1,270		1,270
Power Segment:
Letter of credit account	5,990		5,983
Corporate Segment:
Postretirement medical benefit bonds	8,593		7,039
Workers’ compensation bonds	6,590		6,492
Total restricted investments and bond collateral	$	87,209	$	58,305

Carrying value and estimated fair value of restricted investments and bond collateral

The Company’s carrying value and estimated fair value of its restricted investments and bond collateral at December 31, 2012 are as follows:

	Carrying Value		Fair Value
	(In thousands)
Cash and cash equivalents	$	74,607	$	74,607
Time deposits	8,428		8,428
Held-to-maturity securities	3,983		4,339
Available-for-sale securities	191		191
	$	87,209	$	87,565

Amortized cost, gross unrealized holding gains and losses and fair value of held-to-maturity securities

The amortized cost, gross unrealized holding gains and losses and fair value of held-to-maturity securities are as follows:

	December 31,
	2012		2011
	(In thousands)
Amortized cost	$	3,983	$	4,866
Gross unrealized holding gains	356		413
Gross unrealized holding losses	—		(38		)
Fair value	$	4,339	$	5,241

Maturities of held-to-maturity securities

Maturities of held-to-maturity securities are as follows at December 31, 2012:

	Amortized Cost		Fair Value
	(In thousands)
Due within one year	$	609	$	616
Due in five years or less	1,920		2,032
Due after five years to ten years	844		1,017
Due in more than ten years	610		674
	$	3,983	$	4,339

Cost basis, gross unrealized holding gains and fair value of available-for-sale securities

The cost basis, gross unrealized holding gains and fair value of available-for-sale securities are as follows:

	December 31,
	2012		2011
	(In thousands)
Cost basis	$	175	$	1,566
Gross unrealized holding gains	16		221
Fair value	$	191	$	1,787