Equity - Summary of activity under Employee Stock Purchase Plan (Details) (Employee Stock Purchase Plan [Member], USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period (shares)	467,960	458,694	391,108	433,452
Granted (shares)	0	0	275,655	246,717
Exercised (shares)	(10,818)	(13,490)	(29,320)	(53,005)
Forfeited (shares)	(16,671)	(11,403)	(39,097)	(22,812)
Expired (shares)	0	0	(157,875)	(170,551)
Outstanding and exercisable, end of period (shares)	440,471	433,801	440,471	433,801
General and Administrative Expense
Summary of the Employee Stock Purchase Plan activity
Share-based compensation expense			$ 0.2