Fair Value of Financial Instruments and Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2013

Fair Value Disclosures [Abstract]

Schedule of fair values of financial instruments

	September 30, 2013
	Carrying Amount		Total Fair Value		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
6.25% senior notes due 2021	$	700,000	$	570,500	$	570,500	$	—	$	—
6.00% senior notes due 2019	800,000		666,000		666,000		—		—
9.75% senior notes due 2018(4)	496,214		511,875		511,875		—		—
Term loan due 2020(5)	618,911		608,480		—		608,480		—
3.75% convertible senior notes due 2017(6)	287,337		337,376		337,376		—		—
3.25% convertible senior notes due 2015(2)	296,942		285,432		285,432		—		—
2.375% convertible senior notes due 2015(3)	93,114		95,303		95,303		—		—
Total long-term debt	$	3,292,518	$	3,074,966	$	2,466,486	$	608,480	$	—

	December 31, 2012
	Carrying Amount		Total Fair Value		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
6.25% senior notes due 2021	$	700,000	$	649,110	$	649,110	$	—	$	—
6.00% senior notes due 2019	800,000		755,600		755,600		—		—
9.75% senior notes due 2018(4)	495,161		540,125		540,125		—		—
Term loan due 2016(1)	539,481		537,316		—		537,316		—
3.25% convertible senior notes due 2015(2)	515,901		513,375		513,375		—		—
2.375% convertible senior notes due 2015(3)	249,306		268,094		268,094		—		—
Total long-term debt	$	3,299,849	$	3,263,620	$	2,726,304	$	537,316	$	—

⁽¹⁾  Net of debt discount of $519 as of December 31, 2012.

⁽²⁾  Net of debt discount of $8,332 and $20,261 as of September 30, 2013 and December 31, 2012, respectively.

⁽³⁾  Net of debt discount of $9,584 and $38,194 as of September 30, 2013 and December 31, 2012, respectively.

⁽⁴⁾  Net of debt discount of $3,786 and $4,839 as of September 30, 2013 and December 31, 2012, respectively.

⁽⁵⁾  Net of debt discount of $2,964 as of September 30, 2013.

⁽⁶⁾  Net of debt discount of $57,663 as of September 30, 2013.

Schedule of fair value of assets and liabilities measured on recurring and nonrecurring basis

	September 30, 2013
	Total Fair Value		Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Financial assets (liabilities):
U.S. treasury and agency securities	$	97,097	$	97,097	$	—	$	—
Mutual funds held in Rabbi Trust	$	8,830	$	8,830	$	—	$	—
Corporate debt securities	$	255,874	$	—	$	255,874	$	—
Forward coal sales	$	9,004	$	—	$	9,004	$	—
Commodity swaps	$	6,118	$	—	$	6,118	$	—

	December 31, 2012
	Total Fair Value			Quoted Prices in Active Markets (Level 1)		Significant Other Observable Inputs (Level 2)			Significant Unobservable Inputs (Level 3)
Financial assets (liabilities):
U.S. treasury and agency securities	$	85,568		$	85,568	$	—		$	—
Mutual funds held in Rabbi Trust	$	8,133		$	8,133	$	—		$	—
Corporate debt securities	$	212,639		$	—	$	212,639		$	—
Forward coal sales	$	15,359		$	—	$	15,359		$	—
Forward coal purchases	$	(4	)	$	—	$	(4	)	$	—
Commodity swaps	$	7,080		$	—	$	7,080		$	—
Commodity options	$	138		$	—	$	138		$	—