Common Stock - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended														12 Months Ended					12 Months Ended					12 Months Ended					12 Months Ended				12 Months Ended		12 Months Ended										12 Months Ended				12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Special Cash Dividend	Dec. 31, 2012 2005 Employees' Restricted Stock Purchase Plan	Dec. 31, 2011 2005 Employees' Restricted Stock Purchase Plan	Dec. 31, 2010 2005 Employees' Restricted Stock Purchase Plan	Dec. 31, 2012 2001 Employees' Restricted Stock Purchase Plan	Dec. 31, 2011 2001 Employees' Restricted Stock Purchase Plan	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan	Dec. 31, 2012 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board	Dec. 31, 2011 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board	Mar. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board	Dec. 31, 2012 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2009 Issuance	Dec. 31, 2011 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2009 Issuance	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2009 Issuance	Dec. 31, 2009 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2009 Issuance	Mar. 31, 2009 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2009 Issuance	Dec. 31, 2012 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2008 Issuance	Dec. 31, 2011 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2008 Issuance	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2008 Issuance	Dec. 31, 2009 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2008 Issuance	Mar. 31, 2008 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer First Quarter of 2008 Issuance	Dec. 31, 2011 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer Fourth quarter of 2007 Issuance	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer Fourth quarter of 2007 Issuance	Dec. 31, 2009 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer Fourth quarter of 2007 Issuance	Dec. 31, 2008 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer Fourth quarter of 2007 Issuance	Dec. 31, 2007 2001 Employees' Restricted Stock Purchase Plan Chief Executive Officer Fourth quarter of 2007 Issuance	Dec. 31, 2012 2001 Employees' Restricted Stock Purchase Plan Various Employees	Dec. 31, 2011 2001 Employees' Restricted Stock Purchase Plan Various Employees	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Various Employees	Dec. 31, 2007 2001 Employees' Restricted Stock Purchase Plan Various Employees	Dec. 31, 2010 2001 Employees' Restricted Stock Purchase Plan Various Officers And Employees Fourth Quarter of 2006 Issuance	Dec. 31, 2006 2001 Employees' Restricted Stock Purchase Plan Various Officers And Employees Fourth Quarter of 2006 Issuance	Dec. 31, 2012 Class B	Dec. 31, 2012 Class B 2010 Employees' Restricted Stock Purchase Plan	Dec. 31, 2011 Class B 2010 Employees' Restricted Stock Purchase Plan	Dec. 31, 2011 Class B 2010 Employees' Restricted Stock Purchase Plan Third Anniversary Of Grant Date	Dec. 31, 2011 Class B 2010 Employees' Restricted Stock Purchase Plan Fourth Anniversary Of Grant Date	Dec. 31, 2012 Class B 2010 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board	Dec. 31, 2012 Class B 2010 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board First Anniversary	Dec. 31, 2012 Class B 2010 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board Second Anniversary	Dec. 31, 2012 Class B 2010 Employees' Restricted Stock Purchase Plan Chief Executive Officer ("CEO") And Chairman Of The Board Third Anniversary	Dec. 31, 2010 Class B 2001 Employees' Restricted Stock Purchase Plan	Dec. 31, 2012 Stock Incentive Plan	Dec. 31, 2011 Stock Incentive Plan	Dec. 31, 2010 Stock Incentive Plan	Dec. 31, 2012 Stock Incentive Plan Class B	Dec. 31, 2012 Long Term Incentive Plans	Dec. 31, 2011 Long Term Incentive Plans	Dec. 31, 2010 Long Term Incentive Plans	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2010 Stock Options	Dec. 31, 2012 Restricted Stock	Dec. 31, 2011 Restricted Stock	Dec. 31, 2010 Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividends declared and paid, per share									$ 0.60	$ 0.20	$ 0.20	$ 0.40
Dividends declared and paid									$ 58,300,000	$ 19,000,000	$ 19,000,000	$ 38,900,000
Stock repurchase programs authorized to purchase, shares	10,000,000								10,000,000
Compensation cost recognized, pre-tax charge																																																													20,100,000	15,800,000	13,300,000
Compensation cost recognized, after-tax																																																													12,500,000	9,800,000	8,300,000	1,400,000	1,200,000	2,000,000
Earnings per share diluted	$ 1.39	$ 0.73	$ 1.10	$ 1.31	$ 0.98	$ 0.86	$ 1.04	$ 1.15	$ 4.53	$ 4.04	$ 2.34																																																		$ 0.13	$ 0.10	$ 0.08
Compensation cost recognized																																																																2,300,000	2,000,000	3,100,000
Shares reserved																																												6,000,000									2,400,000				23,000,000
Stock options granted during period (net of cancellations)									2,966,850	2,894,500	94,000																																											2,760,050	2,561,250	69,500
Weighted-average grant date fair value of option granted																																																						$ 10.73	$ 11.62	$ 7.84
Total in-the-money value of all stock options exercised during the year									54,400,000	28,900,000	26,800,000
Stock issued under employee stock purchase plan													117,901	98,366	94,955
Percentage of discount provided to eligible employees for purchase of shares under employee stock purchase plan													10.00%
Compensation cost recognized									22,518,000	18,225,000	16,799,000		533,000	461,000	339,000				375,000	375,000	355,000		556,000	556,000	556,000	482,000		15,000	375,000	375,000			333,000	375,000				42,000	120,000	135,000		1,300,000			370,000	198,000			1,000,000									2,800,000	2,400,000	3,500,000	20,100,000	15,800,000	13,300,000
Stock issued during period, net of cancellations									900,000									1,200,000
Issuance of restricted shares approved, shares																						49,472					109,850					62,190					61,362				22,250		247,000			21,500			54,127
Restricted shares price, per share																						$ 30.32					$ 20.26					$ 24.12					$ 24.45				$ 29.62		$ 25.71			$ 53.21			$ 36.95
Issuance of restricted shares, value																						1,500,000					2,200,000					1,500,000					1,500,000				659,000		6,400,000			1,100,000			2,000,000
Restricted Stock Purchase Plan, annual vesting percentage																																																		50.00%	25.00%	25.00%
Estimated compensation cost																			$ 395,000				$ 74,000																							$ 537,000			$ 1,000,000
Fully vested shares									1,845,249							62,044	78,133	313,770	12,368				27,462	27,462	27,463			15,548	15,546	15,548	15,548		15,341	15,341	15,340	15,340									750		20,000	20,000
Number of shares cancelled																																													750
Stock-based compensation plans expired																		2010-03
Issuance upon conversion of shares																																												28,083,325