Stockholders' Equity (Details) (USD $) In Thousands, except Share data, unless otherwise specified	1 Months Ended		6 Months Ended	12 Months Ended					12 Months Ended													12 Months Ended													1 Months Ended			12 Months Ended				1 Months Ended			12 Months Ended
	Jun. 30, 2012	Feb. 29, 2012	Jun. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	May 31, 2010 Maximum	May 31, 2010 Minimum	Dec. 31, 2012 Nonvested stock units issued (NSUs) Y	Dec. 31, 2011 Nonvested stock units issued (NSUs)	Dec. 31, 2010 Nonvested stock units issued (NSUs)	Dec. 31, 2012 Restricted Stock Units (RSUs) Y	Dec. 31, 2011 Restricted Stock Units (RSUs)	Dec. 31, 2010 Restricted Stock Units (RSUs)	Dec. 31, 2012 Directors' shares	Dec. 31, 2011 Directors' shares	Dec. 31, 2010 Directors' shares	Dec. 31, 2012 Stock Appreciation Rights (SARs) Y	Dec. 31, 2011 Stock Appreciation Rights (SARs) Y	Dec. 31, 2010 Stock Appreciation Rights (SARs)	Dec. 31, 2012 2006 Equity Incentive Plan (2006 Plan)	Dec. 31, 2012 2006 Equity Incentive Plan (2006 Plan) Nonvested stock units issued (NSUs)	Dec. 31, 2011 2006 Equity Incentive Plan (2006 Plan) Nonvested stock units issued (NSUs)	Dec. 31, 2010 2006 Equity Incentive Plan (2006 Plan) Nonvested stock units issued (NSUs)	Dec. 31, 2012 2006 Equity Incentive Plan (2006 Plan) Nonvested stock units issued (NSUs) Award granted in 2011	Dec. 31, 2012 2006 Equity Incentive Plan (2006 Plan) Nonvested stock units issued (NSUs) Award granted in 2012	Dec. 31, 2012 2006 Equity Incentive Plan (2006 Plan) Restricted Stock Units (RSUs)	Dec. 31, 2011 2006 Equity Incentive Plan (2006 Plan) Restricted Stock Units (RSUs)	Dec. 31, 2010 2006 Equity Incentive Plan (2006 Plan) Restricted Stock Units (RSUs)	Dec. 31, 2012 2006 Equity Incentive Plan (2006 Plan) Stock Appreciation Rights (SARs) Y	Dec. 31, 2011 2006 Equity Incentive Plan (2006 Plan) Stock Appreciation Rights (SARs) Y	Dec. 31, 2010 2006 Equity Incentive Plan (2006 Plan) Stock Appreciation Rights (SARs) Y	Dec. 31, 2009 2006 Equity Incentive Plan (2006 Plan) Stock Appreciation Rights (SARs) Y	Dec. 31, 2012 2012 LTIP Awards	May 31, 2012 2012 LTIP Awards Maximum	May 31, 2012 2012 LTIP Awards Minimum	May 31, 2012 2012 LTIP Awards Restricted Stock Units (RSUs)	Dec. 31, 2012 2012 LTIP Awards Restricted Stock Units (RSUs)	Dec. 31, 2012 2012 LTIP Awards Restricted Stock Units (RSUs) Maximum	Dec. 31, 2012 2012 LTIP Awards SAR awards and RSU awards	Dec. 31, 2012 Long-term incentive award (Level III Awards)	Jun. 30, 2011 Long-term incentive award (Level III Awards) Maximum	Jun. 30, 2011 Long-term incentive award (Level III Awards) Minimum	Jun. 30, 2011 Long-term incentive award (Level III Awards) Restricted Stock Units (RSUs)	Dec. 31, 2011 Long-term incentive award (Level III Awards) Restricted Stock Units (RSUs)	Dec. 31, 2011 Long-term incentive award (Level III Awards) Restricted Stock Units (RSUs) Maximum
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
Portion of SAR and RSU awards scheduled to vest on December 31, 2010 and December 31, 2011																																								one-half
Portion of SAR and RSU awards scheduled to vest on December 31, 2015 and December 31, 2016																																								one-half
Percentage of portion of SAR and RSU awards scheduled to vest on December 31, 2010																																								80.00%
Percentage of portion of SAR and RSU awards scheduled to vest on December 31, 2011																																								20.00%
Percentage of portion of SAR and RSU awards scheduled to vest on December 31, 2015																																								80.00%
Percentage of portion of SAR and RSU awards scheduled to vest on December 31, 2016																																								20.00%
Maximum contractual term of SARs with final vesting date of December 31, 2011 (in years)																			10
Maximum contractual term of SARs with final vesting date of December 31, 2016 (in years)																			15
Authorized number of shares of common stock				125,000,000	125,000,000		125,000,000	50,000,000
Maximum stock repurchase amount approved by Board of Directors	$ 200,000	$ 100,000
Remaining stock repurchase amount approved by Board of Directors				79,300
Number of shares repurchased			1,749,000	2,765,000
Repurchase of common stock, payments			100,000	120,700
Average stock price of shares repurchased (in dollars per share)			$ 57.16	$ 43.66
Number of shares granted																						209,000	199,000	315,000			352,000	275,000											352,000							275,000
NSUs granted that will vest at the end of each of the three years after the performance goals are achieved (as a percent)																									33.30%	33.30%
Award vesting period																									3 years	3 years
Compensation expense cumulative amount based on maximum number of units subject to performance objectives probable																																		3,000							8,000
Stock compensation expenses
Compensation expenses recorded				14,661	14,803	12,782			11,849	11,719	7,915	231	305	677	1,080	966	770	1,501	1,813	3,420
Income tax benefit recognized				(5,573)	(5,788)	(5,127)
Net compensation expenses				9,088	9,015	7,655
Unrecognized Compensation Cost				12,413					6,780			750						4,883
Weighted-Average Remaining Vesting Period (in years)									0.6			3.2						3.2
Maximum compensation cost excluded from unrecognized compensation cost subject to performance condition not considered probable																																		19,717							20,591
Nonvested Stock Units and Restricted Stock Units Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)																						677,000	798,000	717,000			319,000	85,000	159,000	760,000	1,125,000	1,200,000
Granted (in shares)																						209,000	199,000	315,000			352,000	275,000											352,000							275,000
Vested (in shares)																						(297,000)	(263,000)	(208,000)				(16,000)	(64,000)
Forfeited (in shares)																						(18,000)	(57,000)	(26,000)				(25,000)	(10,000)			(75,000)
Nonvested at the end of the period (in shares)																						371,000	677,000	798,000			671,000	319,000	85,000	745,000	760,000	1,125,000
Weighted-Average Grant-Date Fair Value
Nonvested at the beginning of the period (in dollars per share)																						$ 48.14	$ 35.61	$ 26.34			$ 70.15	$ 26.73	$ 26.73
Granted (in dollars per share)																						$ 63.18	$ 87.50	$ 45.99			$ 56.12	$ 82.09										$ 56.12							$ 82.09
Vested (in dollars per share)																						$ 35.90	$ 40.31	$ 22.83				$ 26.73	$ 26.73
Forfeited (in dollars per share)																						$ 63.68	$ 46.61	$ 25.98				$ 82.09	$ 26.73
Nonvested at the end of the period (in dollars per share)																						$ 58.51	$ 48.14	$ 35.61			$ 62.80	$ 70.15	$ 26.73
Stock Appreciation Rights Issued Under the 2006 Plan
Nonvested at the beginning of the period (in shares)																						677,000	798,000	717,000			319,000	85,000	159,000	760,000	1,125,000	1,200,000
Granted (in shares)																						209,000	199,000	315,000			352,000	275,000											352,000							275,000
Exercised (in shares)																														(15,000)	(365,000)
Forfeited (in shares)																						(18,000)	(57,000)	(26,000)				(25,000)	(10,000)			(75,000)
Nonvested at the end of the period (in shares)																						371,000	677,000	798,000			671,000	319,000	85,000	745,000	760,000	1,125,000
Exercisable at the end of the period (in shares)																														220,000
Expected to vest and exercisable (in shares)																														707,945
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)																														$ 26.73	$ 26.73	$ 26.73
Exercised (in dollars per share)																														$ 26.73	$ 26.73
Forfeited (in dollars per share)																																$ 26.73
Outstanding at the end of the period (in dollars per share)																														$ 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)																														7.9	8.8	8.7	9.8
Exercisable at the end of the period (in years)																														4.4
Expected to vest and exercisable (in years)																														7.8
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)																														10,087	37,118	59,636	8,608
Exercisable at the end of the period (in dollars)																														2,979
Expected to vest and exercisable (in dollars)																														9,586
Stock appreciation rights exercisable during period (in shares)																															120,000
Number of shares receivable as right under stock-based awards																																					1							1
Revenue targets to be met for awards to be vested																																			$ 2,900,000	$ 2,200,000						$ 2,500,000	$ 1,825,000
Diluted earnings per share targets to be met for awards to be vested (in dollars per share)																																			$ 10.50	$ 7.00						$ 9.60	$ 7.00