Consolidated Statements of Changes in Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Marathon PGM [Member]	Benton Resources [Member]	Peregrine Metals Ltd. [Member]	Common Stock [Member]	Common Stock [Member] Marathon PGM [Member]	Common Stock [Member] Benton Resources [Member]	Common Stock [Member] Peregrine Metals Ltd. [Member]	Additional Paid-in Capital [Member]	Additional Paid-in Capital [Member] Marathon PGM [Member]	Additional Paid-in Capital [Member] Benton Resources [Member]	Additional Paid-in Capital [Member] Peregrine Metals Ltd. [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Noncontrolling Interest [Member]
BALANCE, beginning of year at Dec. 31, 2009	$ 446,811				$ 967				$ 674,869				$ (228,935)	$ (90)	$ 0
BALANCE, beginning of year (in shares) at Dec. 31, 2009					96,732,000
Increase (Decrease) in Equity [Roll Forward]
Net income	50,365												50,365		0
Change in fair market value of securities	(762)													(762)
Common stock issued under employee benefit plans (in shares)					319,000
Common stock issued under employee benefit plans	4,445				3				4,442
Stock option expense	160								160
Common stock issued under stock plans (in shares)	89,971				90,000
Common stock issued under stock plans	844				1				843
Common stock issued under Directors’ deferral plan (in shares)					3,000
Common stock issued under Directors’ deferral plan	75								75
Nonvested shares of common stock granted to officers and employees (in shares)					856,000
Nonvested shares of common stock granted to officers and employees	9				9
Common stock issued for acquisition (in shares)						3,882,000
Common stock issued for acquisition		73,448				39				73,409
Amortization of unearned nonvested stock	7,775								7,775
Forfeiture of nonvested stock	(98)								(98)
BALANCE, end of year at Dec. 31, 2010	583,072				1,019				761,475				(178,570)	(852)	0
BALANCE, end of year (in shares) at Dec. 31, 2010					101,882,000
Increase (Decrease) in Equity [Roll Forward]
Net income	144,295												144,295		0
Change in fair market value of securities	(109)													(109)
Common stock issued under employee benefit plans (in shares)					371,000
Common stock issued under employee benefit plans	5,622				4				5,618
Stock option expense	231								231
Common stock issued under stock plans (in shares)	52,131				52,000
Common stock issued under stock plans	787				0				787
Common stock issued under Directors’ deferral plan (in shares)					7,000
Common stock issued under Directors’ deferral plan	81								81
Nonvested shares of common stock granted to officers and employees (in shares)					686,000
Nonvested shares of common stock granted to officers and employees	7				7
Common stock issued for acquisition (in shares)							348,000	12,030,000
Common stock issued for acquisition			6,919	96,652			4	120			6,915	96,532
Amortization of unearned nonvested stock	6,453								6,453
Forfeiture of nonvested stock	(42)								(42)
BALANCE, end of year at Dec. 31, 2011	843,968				1,154				878,050				(34,275)	(961)	0
BALANCE, end of year (in shares) at Dec. 31, 2011	115,375,604				115,376,000
Increase (Decrease) in Equity [Roll Forward]
Net income	54,416												55,045		(629)
Change in fair market value of securities	862													862
Common stock issued under employee benefit plans (in shares)					749,000
Common stock issued under employee benefit plans	7,898				8				7,890
Income tax benefit on share-based compensation	7,737								7,737
Stock option expense	97								97
Common stock issued under stock plans (in shares)	16,552				74,000
Common stock issued under stock plans	44				1				43
Common stock issued under Directors’ deferral plan (in shares)					12,000
Common stock issued under Directors’ deferral plan	76								76
Nonvested shares of common stock granted to officers and employees (in shares)					740,000
Nonvested shares of common stock granted to officers and employees	54				7				47
Equity component of 1.75% Convertible debenture	137,173								137,173
Noncontrolling interest	93,821								41,431						52,390
Valuation allowance	35,799								35,799
Deferred taxes on 1.75% convertible debenture	(57,526)								(57,526)
Amortization of unearned nonvested stock	8,341								8,341
Forfeiture of nonvested stock	(180)								(180)
BALANCE, end of year at Dec. 31, 2012	$ 1,132,580				$ 1,170				$ 1,058,978				$ 20,770	$ (99)	$ 51,761
BALANCE, end of year (in shares) at Dec. 31, 2012	116,951,081				116,951,000