Condensed Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized	2,000,000	2,000,000
Preferred stock, shares outstanding	0	0
Class A
Capital stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	100,000,000	100,000,000
Common Stock, shares issued	52,672,162	52,428,423
Common Stock, shares outstanding	52,672,162	52,428,423
Class B
Capital stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	3,000,000	3,000,000
Common Stock, shares issued	1,763,866	1,763,866
Common Stock, shares outstanding	1,763,866	1,763,866
Common Stock, liquidation preference (in dollars per share)	$ 0.50	$ 0.50
Senior Notes 10.25 Percent Due 2014
Interest rate on debt instrument (as a percent)	10.25%	10.25%
6.75% Senior notes due 2020
Interest rate on debt instrument (as a percent)	6.75%	6.75%
6.375% Senior notes due 2022
Interest rate on debt instrument (as a percent)	6.375%	6.375%
Senior Notes 10.25 Percent Due 2014
Interest rate on debt instrument (as a percent)	10.25%	10.25%
10.25% Senior notes due 2014, unamortized discount (in dollars)	$ 1,553	$ 2,340