Stockholders' Equity (Details) (USD $)	3 Months Ended					6 Months Ended		12 Months Ended	183 Months Ended		3 Months Ended																3 Months Ended
	Jun. 30, 2014 IncentivePlan	Jun. 30, 2013	Mar. 31, 2013	Jun. 30, 2012	Mar. 31, 2012	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013	Jun. 30, 2014	Feb. 05, 2013	Jun. 30, 2014 Q1 [Member]	Mar. 31, 2013 Q1 [Member]	Jun. 30, 2014 Q2 [Member]	Jun. 30, 2013 Q2 [Member]	Jun. 30, 2014 Q3 [Member]	Sep. 30, 2013 Q3 [Member]	Jun. 30, 2014 Q4 [Member]	Dec. 31, 2013 Q4 [Member]	Jun. 30, 2014 Restricted Stock [Member]	Jun. 30, 2013 Quarterly Dividend [Member]	Mar. 31, 2013 Quarterly Dividend [Member]	Jun. 30, 2012 Quarterly Dividend [Member]	Mar. 31, 2012 Quarterly Dividend [Member]	Jun. 30, 2014 Class A [Member] VoteperShare	Dec. 31, 2013 Class A [Member]	Jun. 30, 2013 Class A [Member]	Jun. 30, 2014 Class B [Member] VoteperShare	Dec. 31, 2013 Class B [Member]	Jun. 30, 2013 Class B [Member]
Stockholders' Equity [Abstract]
Shares outstanding (in shares)	25,900,000	25,600,000				25,900,000	25,600,000	26,100,000	25,900,000															6,572,864	6,701,930	6,095,806	19,325,820	19,384,174	19,534,174
Dividends Payable [Line Items]
Dividends declared (in dollars per share)	$ 0.06	$ 0.05				$ 0.12	$ 0.10													$ 0.06	$ 0.06	$ 0.05	$ 0.05
Dividend payment date		Jun. 24, 2014	Mar. 25, 2014	Jun. 25, 2013	Mar. 26, 2013
Dividend record date		Jun. 10, 2014	Mar. 11, 2014	Jun. 11, 2013	Mar. 12, 2013
Voting Rights [Abstract]
Number of votes per share																								1			10
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			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
RSA shares outstanding (in shares)	564,250					564,250		566,950	564,250
Average weighted grant price (in dollars per share)						$ 63.93		$ 63.93
Percentage stock based compensation expense recognize over three years vesting period (in hundredths)	30.00%																		60.00%
Percentage stock based compensation expense recognize over five years vesting period (in hundredths)	70.00%																		40.00%
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
RSAs granted (in shares)																			2,100
Restricted stock award shares approved grant date fair value (in dollars per share)																			$ 81.99
Vesting Period For Recognition Of 60 Percent Of Stock Based Compensation Expense																			3 years
Vesting period for recognition of 40 percent of stock based compensation expense																			5 years
Actual and projected stock based compensation expense for RSA shares and options [Abstract]
Actual stock based compensation expense	$ 1,697,000	$ 15,000				$ 3,397,000	$ 29,000					$ 15,000
Projected stock based compensation expense 2013	2,072,000													15,000		741,000		1,301,000
Projected stock based compensation expense 2014	6,791,000										1,700,000		1,697,000		1,697,000		1,697,000
Projected stock based compensation expense 2015	6,777,000										1,695,000		1,694,000		1,694,000		1,694,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Three	5,805,000										1,694,000		1,694,000		1,339,000		1,078,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Ten	117,000										50,000		50,000		17,000		0
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Six	1,158,000										325,000		325,000		268,000		240,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Seven	840,000										240,000		240,000		192,000		168,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Nine	328,000										105,000		105,000		68,000		50,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Four	3,395,000										903,000		903,000		816,000		773,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Five	2,798,000										771,000		771,000		702,000		554,000
Employee Service Share Based Compensation Nonvested Awards Projected Compensation Cost Year Eight	567,000										168,000		168,000		126,000		105,000
Compensation cost related to non-vested restricted stock awards and options not yet recognized	25,200,000					25,200,000			25,200,000
Stock options exercised (in shares)	20,000	0				40,000	2,623
Proceeds from exercise of stock options	792,000					1,637,000	76,000
Tax benefit from exercise of stock options	$ 175,000					$ 349,000	$ 16,000
Stock Repurchase Program [Abstract]
Incremental Class A shares authorized to buyback (in shares)										500,000
Shares repurchased (in shares)	103,528	81,726				224,720	118,402		8,936,313
Average price per share of repurchased shares (in dollars per share)	$ 77.76	$ 52.73				$ 78.75	$ 52.99		$ 43.17
Share available under program to repurchase (in shares)	698,495					698,495			698,495