Shareholders' Equity and Common Stock Equivalents (Details 3) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2012
Summary of changes in outstanding restricted common stock units
Beginning balance, Total Outstanding, Units	1,663,190		1,423,611
Granted, Total Outstanding Units	264,064	[1]
Vested, Total Outstanding Units	0
Forfeited, Total Outstanding Units	(66,560)
Distributed, Total Outstanding Units	(270,556)	[2]
Ending balance, Total Outstanding, Units	1,590,138		1,423,611
Beginning balance, Total Outstanding, Weighted Average Grant Date Fair Value per Unit	$ 19.41
Grant, Total Outstanding, Weighted Average Grant Date Fair Value per Unit	$ 28.19	[1]
Vested, Total Outstanding, Weighted Average Grant Date Fair Value per Unit	$ 0
Forfeited, Total Outstanding, Weighted Average Grant Date Fair Value per Unit	$ 18.36
Distributed, Total Outstanding, Weighted Average Grant Date Fair Value per Unit	$ 16.91	[2]
Ending balance, Total Outstanding, Weighted Average Grant Date Fair Value per Unit	$ 21.34
Beginning balance, Vested, Units	675,159
Granted, Vested, Units	0	[1]
Vested Units	448,451
Forfeited, Vested, Units	0
Distributed, Vested, Units	(270,556)	[2]
Ending balance, Vested, Units	853,054
Beginning balance, Vested, Weighted Average Grant Date Fair Value per Unit	$ 12.56
Granted, Weighted Average Grant Date Fair Value per Unit	$ 0	[1]
Vested, Weighted Average Grant Date Fair Value per Unit	$ 18.60
Forfeited, Weighted Average Grant Date Fair Value per Unit	$ 0
Distributed, Vested, Weighted Average Grant Date Fair Value per Unit	$ 16.91	[2]
Ending balance, Vested, Weighted Average Grant Date Fair Value per Unit	$ 14.36

[1] Includes dividends reinvested into additional restricted common stock units.

[2] Includes distributed units which were utilized to satisfy withholding taxes due on the distribution.