Stock Incentive Plans (Details) (USD $)	3 Months Ended		9 Months Ended				9 Months Ended		9 Months Ended								0 Months Ended				6 Months Ended	9 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Restricted common stock	Dec. 31, 2013 Restricted common stock	Sep. 30, 2014 Performance-based restricted stock units	Dec. 31, 2013 Performance-based restricted stock units	Sep. 30, 2014 Performance-based restricted stock units Vest on February 1, 2017, performance level one	Sep. 30, 2014 Performance-based restricted stock units Vest on February 1, 2017, performance level two	Sep. 30, 2014 Performance-based restricted stock units Vest on February 1, 2017, performance level three	Sep. 30, 2014 Performance-based restricted stock units Vest on February 1, 2017, performance level four	Sep. 30, 2014 Performance-based restricted stock units Vest on February 1, 2017, performance level five	Sep. 30, 2014 Restricted common stock and restricted stock units	Sep. 30, 2014 Performance-based restricted common stock and performance-based restricted stock units	Sep. 30, 2014 Performance-based restricted common stock	May 21, 2014 Employee Stock Plan, 2014 Plan	Sep. 30, 2014 Employee Stock Plan, 2014 Plan	Sep. 30, 2014 Employee Stock Plan, 2005 Plan	May 21, 2014 Employee Stock Plan, 2005 Plan	Jun. 30, 2014 Employee Stock Plan, 2005 Plan Restricted common stock	Sep. 30, 2014 Employee Stock Plan, 2005 Plan Restricted common stock	Sep. 30, 2014 Employee Stock Plan, 2005 Plan Restricted common stock Shares vesting in December 2014	Sep. 30, 2014 Employee Stock Plan, 2005 Plan Restricted common stock Shares vesting in December 2015	Sep. 30, 2014 Employee Stock Plan, 2005 Plan Restricted common stock Shares vesting in December 2016	Jun. 30, 2014 Employee Stock Plan, 2005 Plan Performance-based restricted stock units	Sep. 30, 2014 Employee Stock Plan, 2005 Plan Performance-based restricted stock units	Sep. 30, 2014 Directors Stock Plan, 2007 Plan Restricted common stock	Sep. 30, 2014 Directors Stock Plan, 2007 Plan Restricted common stock Vesting in February 2017
Stock Incentive Plans
Additional shares authorized for future grants																	3,250,000
Shares available for future grants																		3,757,925	0	507,925
Forfeited (in shares)					23,590		20,600															9,420
Share of common stock to be paid for each restricted stock unit																											1
Shares to be issued on vest date as percentage of units granted based on actual performance									125.00%	100.00%	75.00%	50.00%	0.00%
Shares to be issued as a percentage of units granted in the event of change in control									100.00%
Vesting percentage																													100.00%
Outstanding (in shares)					1,132,232	781,644	784,400	409,100																			386,300	28,148
Restricted common stock granted (in shares)					429,346		395,900														396,840		128,340	128,940	130,140	395,900		32,506
Vested (in shares)					55,168
Granted (in dollars per share)					$ 12.63		$ 12.14
Stock-based compensation expense, net of taxes	$ 1,400,000	$ 1,200,000	$ 4,200,000	$ 3,400,000
Stock-based compensation expense, taxes	789,000	636,000	2,300,000	1,900,000
Pre-tax compensation cost related to share-based compensation awards not yet recognized														12,400,000
Pre-tax compensation cost, weighted average recognition period														1 year 10 months 25 days
Pre-tax compensation cost related to non-vested performance-based stock awards and units															$ 1,800,000
Restricted shares or units for which compensation cost will be excluded until the achievement of the performance conditions become probable							99,525									65,000