Stock Incentive Plans (Details 2)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Restricted common stock
Stock Incentive Plans
Restricted common stock granted (in shares)	536,110
Unvested at the end of the period (in shares)	781,644	1,146,657
Employee Stock Plan, 2005 Plan | Shares vesting in December 2014
Stock Incentive Plans
Restricted common stock granted (in shares)	156,410	34,500	82,280	99,604
Employee Stock Plan, 2005 Plan | Shares vesting in December 2015
Stock Incentive Plans
Restricted common stock granted (in shares)	157,410	51,500	82,280
Employee Stock Plan, 2005 Plan | Shares vesting in December 2016
Stock Incentive Plans
Restricted common stock granted (in shares)	2,000		65,000
Employee Stock Plan, 2005 Plan | Restricted common stock
Stock Incentive Plans
Restricted common stock granted (in shares)	494,420	155,000	663,530	778,740
Unvested at the end of the period (in shares)	315,820	86,000	229,560	99,604
Employee Stock Plan, 2005 Plan | Performance-based restricted common stock awards or units
Stock Incentive Plans
Restricted common stock granted (in shares)	102,275		65,000