Stockholders' Equity (Details) (USD $)	0 Months Ended	1 Months Ended		3 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended
	Feb. 28, 2015	Jan. 31, 2015	Jun. 30, 2012	Mar. 31, 2014	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Dec. 31, 2011	Dec. 31, 2013 group	May 31, 2012	May 31, 2006
Stockholders' equity
Grant date fair value of RSUs					$ 98.29
Compensation expense cumulative amount based on maximum number of units subject to performance objectives probable					$ 2,000,000
Unrecognized compensation cost					6,100,000
Maximum stock repurchase amount approved by Board of Directors			200,000,000
Number of shares repurchased	3,823,000				377,000
Repurchase of common stock, payments	200,000,000				27,900,000
Average stock price of shares repurchased (in dollars per share)	$ 52.31				$ 74.09
Remaining stock repurchase amount approved by Board of Directors		200,000,000			172,100,000
Stock compensation expenses
Compensation expenses recorded				2,865,000	13,524,000	13,136,000	14,661,000
Income tax benefit recognized				(1,082,000)	(5,143,000)	(4,950,000)	(5,573,000)
Net compensation expenses				1,783,000	8,381,000	8,186,000	9,088,000
Unrecognized Compensation Cost					21,589,000
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Cancelled (in shares)							(200,000)
Weighted-Average Grant-Date Fair Value
Granted (in dollars per share)					$ 98.29
Stock Appreciation Rights Issued Under the 2006 Plan
Granted (in shares)				0		0	0
Forfeited (in shares)				0	0	0
Weighted-Average Exercise Price
Granted (in dollars per share)				$ 0.00	$ 0.00	$ 0.00	$ 0.00
Maximum
Stockholders' equity
Number of shares granted					160,000
Revenue targets to be met for awards to be vested								2,447,000,000
EBITDA targets to be met for awards to be vested								394,000,000
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Granted (in shares)					160,000
Minimum
Stockholders' equity
Revenue targets to be met for awards to be vested								2,155,000,000
EBITDA targets to be met for awards to be vested								336,000,000
Nonvested stock units issued (NSUs)
Stock compensation expenses
Compensation expenses recorded				1,863,000	9,295,000	10,545,000	11,849,000
Unrecognized Compensation Cost					13,917,000
Weighted-Average Remaining Vesting Period (in years)					1 year 6 months
Restricted Stock Units (RSUs)
Stock compensation expenses
Compensation expenses recorded				354,000	1,323,000	287,000	231,000
Unrecognized Compensation Cost					6,317,000
Weighted-Average Remaining Vesting Period (in years)					1 year 6 months
Directors' shares
Stock compensation expenses
Compensation expenses recorded				267,000	1,060,000	1,002,000	1,080,000
Stock Appreciation Rights (SARs)
Stockholders' equity
Maximum contractual term of SARs with final vesting date of December 31, 2011 (in years)					10 years
Maximum contractual term of SARs with final vesting date of December 31, 2016 (in years)					15 years
Stock compensation expenses
Compensation expenses recorded				381,000	1,846,000	1,302,000	1,501,000
Unrecognized Compensation Cost					1,355,000
Weighted-Average Remaining Vesting Period (in years)					10 months 24 days
2006 Equity Incentive Plan (2006 Plan)
Stockholders' equity
Common stock reserved for issuance (in shares)												6,000,000
Maximum number of shares that may be issued through the exercise of incentive stock options												4,500,000
Stock Appreciation Rights Issued Under the 2006 Plan
Forfeited (in shares)							0
Weighted-Average Exercise Price
Forfeited (in dollars per share)				$ 0.00	$ 0.00	$ 0.00	$ 0.00
2006 Equity Incentive Plan (2006 Plan) | Nonvested stock units issued (NSUs)
Stockholders' equity
Number of shares granted				0	196,000	304,000	209,000
Grant date fair value of RSUs				$ 0.00	$ 82.34	$ 57.30	$ 63.18
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)				340,000	331,000	371,000	677,000
Granted (in shares)				0	196,000	304,000	209,000
Vested (in shares)				(2,000)	(142,000)	(315,000)	(297,000)
Forfeited (in shares)				(7,000)	(30,000)	(20,000)	(18,000)
Cancelled (in shares)					(15,000)
Nonvested at the end of the period (in shares)				331,000	340,000	340,000	371,000			340,000
Weighted-Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)				$ 62.23	$ 62.21	$ 58.51	$ 48.14
Granted (in dollars per share)				$ 0.00	$ 82.34	$ 57.30	$ 63.18
Vested (in dollars per share)				$ 58.11	$ 68.39	$ 53.19	$ 35.90
Forfeited (in dollars per share)				$ 64.15	$ 64.18	$ 61.08	$ 63.68
Cancelled (in dollars per share)					$ 84.04		$ 62.17
Nonvested at the end of the period (in dollars per share)				$ 62.21	$ 70.11	$ 62.23	$ 58.51			62.23
Stock Appreciation Rights Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)				340,000	331,000	371,000	677,000
Nonvested at the end of the period (in shares)				331,000	340,000	340,000	371,000			340,000
2006 Equity Incentive Plan (2006 Plan) | Nonvested stock units issued (NSUs) | Award granted in 2011
Stockholders' equity
Awards granted that will vest after the performance goals are achieved (as a percent)					33.33%
Award vesting period					3 years
2006 Equity Incentive Plan (2006 Plan) | Restricted Stock Units (RSUs)
Stockholders' equity
Number of shares granted				0	160,000	156,000	352,000
Grant date fair value of RSUs				$ 0.00	$ 98.29	$ 84.52	$ 56.12
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)				795,000	729,000	671,000	319,000
Granted (in shares)				0	160,000	156,000	352,000
Vested (in shares)				0	0	0	0
Forfeited (in shares)				(66,000)	(35,000)	(32,000)	0
Cancelled (in shares)					(230,000)
Nonvested at the end of the period (in shares)				729,000	624,000	795,000	671,000			795,000
Weighted-Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)				$ 67.03	$ 67.01	$ 62.80	$ 70.15
Granted (in dollars per share)				$ 0.00	$ 98.29	$ 84.52	$ 56.12
Vested (in dollars per share)				$ 0.00	$ 0.00	$ 0.00	$ 0.00
Forfeited (in dollars per share)				$ 67.23	$ 78.39	$ 63.69	$ 0.00
Cancelled (in dollars per share)					$ 82.09
Nonvested at the end of the period (in dollars per share)				$ 67.01	$ 68.82	$ 67.03	$ 62.80			67.03
Stock Appreciation Rights Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)				795,000	729,000	671,000	319,000
Nonvested at the end of the period (in shares)				729,000	624,000	795,000	671,000			795,000
2006 Equity Incentive Plan (2006 Plan) | Stock Appreciation Rights (SARs)
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)				730,000	730,000	745,000	760,000
Nonvested at the end of the period (in shares)				730,000	715,000	730,000	745,000		760,000	730,000
Stock Appreciation Rights Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)				730,000	730,000	745,000	760,000
Granted (in shares)					0
Exercised (in shares)				0	(15,000)	(15,000)	(15,000)
Nonvested at the end of the period (in shares)				730,000	715,000	730,000	745,000		760,000	730,000
Exercisable at the end of the period (in shares)					190,000
Expected to vest and exercisable (in shares)					702,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)				$ 26.73	$ 26.73	$ 26.73	$ 26.73
Exercised (in dollars per share)				$ 0.00	$ 26.73	$ 26.73	$ 26.73
Outstanding at the end of the period (in dollars per share)				$ 26.73	$ 26.73	$ 26.73	$ 26.73		$ 26.73	26.73
Exercisable at the end of the period (in dollars per share)					$ 26.73
Expected to vest and exercisable (in dollars per share)					$ 26.73
Weighted-Average Remaining Contractual Term (in years)
Outstanding at the end of the period (in years)				6 years 8 months 12 days	5 years 9 months 18 days	6 years 11 months 12 days	7 years 10 months 17 days		8 years 9 months 18 days
Exercisable at the end of the period (in years)					2 years 1 month 6 days
Expected to vest and exercisable (in years)					5 years 9 months 18 days
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)				38,690,000	32,990,000	42,143,000	10,087,000		37,118,000	42,143,000
Exercisable at the end of the period (in dollars)					8,767,000
Expected to vest and exercisable (in dollars)					32,396,000
Long-term incentive awards
Stockholders' equity
Compensation expense cumulative amount based on maximum number of units subject to performance objectives probable					12,000,000
Number of participant groups										2
Long-term incentive awards | Award granted in 2012
Stock compensation expenses
Maximum compensation cost excluded from unrecognized compensation cost subject to performance condition not considered probable					15,637,000
Long-term incentive awards | Award Granted in 2013
Stock compensation expenses
Maximum compensation cost excluded from unrecognized compensation cost subject to performance condition not considered probable					10,396,000
Long-term incentive awards | Maximum
Stockholders' equity
Revenue targets to be met for awards to be vested											2,900,000,000
Diluted earnings per share targets to be met for awards to be vested (in dollars per share)											$ 10.50
Long-term incentive awards | Minimum
Stockholders' equity
Revenue targets to be met for awards to be vested											2,200,000,000
Diluted earnings per share targets to be met for awards to be vested (in dollars per share)											$ 7.00
Long-term incentive awards | Restricted Stock Units (RSUs)
Stockholders' equity
Number of shares receivable as right under stock-based awards											1
Grant date fair value of RSUs						$ 84.52	$ 56.12
Weighted-Average Grant-Date Fair Value
Granted (in dollars per share)						$ 84.52	$ 56.12
Long-term incentive awards | Restricted Stock Units (RSUs) | Maximum
Stockholders' equity
Number of shares granted						156,000	352,000
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Granted (in shares)						156,000	352,000
Long-term incentive awards | SAR awards and RSU awards
Stockholders' equity
Portion of SAR and RSU awards scheduled to vest on December 31, 2010 and December 31, 2011					50.00%
Portion of SAR and RSU awards scheduled to vest on December 31, 2015 and December 31, 2016					50.00%
Portion of SAR and RSU awards scheduled to vest on December 31, 2010 and December 31, 2011					50.00%
Portion of SAR and RSU awards scheduled to vest on December 31, 2015 and December 31, 2016					50.00%
Non-revenue Generating Group | Maximum
Stockholders' equity
Revenue targets to be met for awards to be vested										2,558,000,000
EBITDA targets to be met for awards to be vested										415,000,000
Non-revenue Generating Group | Minimum
Stockholders' equity
Revenue targets to be met for awards to be vested										2,290,000,000
EBITDA targets to be met for awards to be vested										372,000,000
Revenue Generating Group | Minimum
Stockholders' equity
EBITDA targets to be met for awards to be vested										350,000,000
Long-term incentive award (Level III Awards) | Restricted Stock Units (RSUs) | Maximum
Stockholders' equity
Number of shares granted									275,000
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Granted (in shares)									275,000
Portion Vesting On December 2010 | Long-term incentive awards | SAR awards and RSU awards
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage					80.00%
Portion Vesting On December 2011 | Long-term incentive awards | SAR awards and RSU awards
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage					20.00%
Portion Vesting On December 2015 | Long-term incentive awards | SAR awards and RSU awards
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage					80.00%
Portion Vesting On December 2016 | Long-term incentive awards | SAR awards and RSU awards
Aggregate Intrinsic Value
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage					20.00%