Shareholders' Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended	6 Months Ended	3 Months Ended		3 Months Ended
	Mar. 31, 2011	Jun. 30, 2012	Jun. 30, 2012 Common Class B [Member]	Dec. 31, 2011 Common Class B [Member]	Jun. 30, 2012 Common Class A [Member]	Dec. 31, 2011 Common Class A [Member]
Class of Stock [Line Items]
Percentage of economic interest held in company (in hundredths)			83.70%	83.70%	16.30%	16.30%
Par value (in dollars per share)			$ 0.000001	$ 0.000001	$ 0.01	$ 0.01
Voting rights			Each share of the Company's Class B common stock entitles its holder to five votes, until the first time that the number of shares of Class B common stock outstanding constitutes less than 20% of the number of all shares of the Company's common stock outstanding.
Voting rights after threshold is crossed (per share)			1
Percentage of outstanding shares rights for distribution (in hundredths)					100.00%
Number of class B units exchanged for equivalent class A common shares (in shares)	536,528
Options Exercised (in shares)			74,271
Amount authorized under stock repurchase program		$ 10
Common stock purchased and retired (in shares)					28,454
Current repurchase authorization at an average price per share (in dollars per share)					$ 4.39