Stock Incentive Plans (Details 2)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Performance based restricted stock unit
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock granted (in shares)	395,900
Unvested at the end of the period (in shares)	776,500	409,100
Restricted common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock granted (in shares)	514,507
Unvested at the end of the period (in shares)	752,701	781,644
Employee Stock Plan | Restricted common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock granted (in shares)	482,001	494,420	155,000	663,530
Unvested at the end of the period (in shares)	341,861	154,040	51,500	144,802
Employee Stock Plan | Restricted common stock | Shares vesting in 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock granted (in shares)	156,137	152,040	51,500	79,802
Employee Stock Plan | Restricted common stock | Shares vesting in 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock granted (in shares)	157,337	2,000		65,000
Employee Stock Plan | Restricted common stock | Shares vesting in 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common stock granted (in shares)	28,387