Stock Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock options
Stock Plans
Term of stock option grants	10 years
Vesting period	4 years
Summary of stock option activity
Outstanding at beginning of the period (in shares)	2,484,844
Granted (in shares)	235,000	226,341	358,000
Exercised (in shares)	(38,005)
Forfeited (in shares)	(386,871)
Expired (in shares)	(114,732)
Outstanding at the end of the period (in shares)	2,180,236	2,484,844
Exercisable at end of the period (vested) (in shares)	1,482,505
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 17.79
Granted (in dollars per share)	$ 10.06	$ 20.45	$ 26.09
Exercised / vested (in dollars per share)	$ 7.09
Forfeited (in dollars per share)	$ 16.77
Expired (in dollars per share)	$ 19.84
Outstanding at the end of the period (in dollars per share)	$ 17.13	$ 17.79
Exercisable at end of the period (vested) (in dollars per share)	$ 16.92
2011 Plan
Stock Plans
Maximum number of shares of common stock with respect to which awards may be granted	2,779,466
Number of shares of common stock available for future grant	1,093,024