Employee Stock Purchase Plan (Details) - Employee Stock Purchase Plan - $ / shares	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2016	Dec. 31, 2014	Dec. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock price (as percentage)		85.00%
Common stock issued to employees of the company	0	50,000	19,000	16,000
Weighted average price per share (in dollars per share)		$ 30.62	$ 71.40	$ 61.60