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		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Summary of the Employee Stock Purchase Plan activity
Outstanding and exercisable, beginning of period (shares)	440,471	433,801	391,108	433,452
Granted (shares)	0	0	275,655	246,717
Exercised (shares)	(11,668)	(7,478)	(40,988)	(60,483)
Forfeited (shares)	(5,219)	(14,007)	(44,316)	(36,819)
Expired (shares)	0	0	(157,875)	(170,551)
Outstanding and exercisable, end of period (shares)	423,584	412,316	423,584	412,316
General and Administrative Expense
Summary of the Employee Stock Purchase Plan activity
Share-based compensation expense			$ 0.2