Stockholders' Equity (Narrative) (Details) (USD $) Share data in Millions, unless otherwise specified	0 Months Ended	3 Months Ended
	Dec. 31, 2014 employee_group	Mar. 31, 2015	Mar. 31, 2014
Components of Stockholders' Equity [Line Items]
Total intrinsic value of options exercised		$ 80,800,000	$ 101,500,000
Cash received from option exercises		$ 10,916,000	$ 32,448,000
Number of employee groups	2
2011 Stock Plan [Member]
Components of Stockholders' Equity [Line Items]
Shares reserved for future issuance		2.7