Stockholders' Equity (Details) (USD $)	1 Months Ended	3 Months Ended					12 Months Ended	168 Months Ended
	Jan. 03, 2012	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2012	Mar. 31, 2013	Feb. 05, 2013
Dividends Payable [Line Items]
Dividends declared (in dollars per share)		$ 0.05				$ 0.04
Dividend payment date		Mar. 26, 2013				Mar. 27, 2012
Dividend record date		Mar. 12, 2013				Mar. 13, 2012
Stock Award and Incentive Plan [Abstract]
Number of incentive plans		2
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares reserved for issuance under each plan, maximum (in shares)		1,500,000						1,500,000
Term of nonqualified stock options, maximum (in years)		10 years
Percentage options granted under plans vest after three years (in hundredths)		75.00%
Percentage options granted under plan vest after four years (in hundredths)		100.00%
Vesting period for 75 percent of stock options		3 years
Vesting period for 100 percent of stock options		4 years
Restricted stock award shares approved grant date fair value (in dollars per share)	$ 43.49
RSA shares outstanding (in shares)						375,000
Average weighted grant price (in dollars per share)							$ 45.14
Percentage stock based compensation expense recognize over three years vesting period (in hundredths)		30.00%
Percentage stock based compensation expense recognize over five years vesting period (in hundredths)		70.00%
Vesting period for recognition of 30 percent of stock based compensation expense (in years)		3 years
Vesting period for recognition of 70 percent of stock based compensation expense (in years)		5 years
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Actual stock based compensation expense	$ 10,100,000	$ 15,000	$ 10,968,000	$ 875,000	$ 869,000	$ 871,000	$ 13,583,000
Projected stock based compensation expense 2013		60,000
Projected stock based compensation expense 2014		16,000
Projected stock based compensation expense 2015		1,000
Compensation cost related to non-vested restricted stock awards and options not yet recognized		62,000						62,000
Stock options exercised (in shares)		2,623
Proceeds from exercise of stock options		76,000				0
Tax benefit from exercise of stock options		16,000				0
Stock Repurchase Program [Abstract]
Incremental Class A shares authorized to buyback (in shares)									500,000
Shares repurchased (in shares)		36,676				224,733		8,520,041
Average price per share of repurchased shares (in dollars per share)		$ 53.57				$ 44.35		$ 41.70
Share available under program to repurchase (in shares)		614,767						614,767
Number of RSA shares approved for granting	105,300
Q1 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Projected stock based compensation expense 2014		7,000
Projected stock based compensation expense 2015		1,000
Q2 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Projected stock based compensation expense 2013		15,000
Projected stock based compensation expense 2014		3,000
Projected stock based compensation expense 2015		0
Q3 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Projected stock based compensation expense 2013		15,000
Projected stock based compensation expense 2014		3,000
Projected stock based compensation expense 2015		0
Q4 [Member]
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Projected stock based compensation expense 2013		15,000
Projected stock based compensation expense 2014		3,000
Projected stock based compensation expense 2015		$ 0
Class A [Member]
Shares outstanding (in shares)		6,147,532	6,121,585			6,592,716	6,121,585	6,147,532
Class B [Member]
Shares outstanding (in shares)		19,564,174	19,624,174			20,040,746	19,624,174	19,564,174
Common Stock [Member]
Shares outstanding (in shares)		25,700,000	25,700,000			26,600,000	25,700,000	25,700,000