Significant Accounting Policies Significant Accounting Policies - Capped Call (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Option indexed to issuers equity cash paid	$ 0	$ 0	$ 48,126,000
Shares received upon settlement of capped call	2.1
Economic value of shares received upon settlement of capped call	140,000,000
Maximum [Member]
option indexed to Company's own stock - strike price	$ 41.05
Option indexed to Issuer's own equity, cap price	$ 56.88
Minimum [Member]
option indexed to Company's own stock - strike price	$ 40.96
Option indexed to Issuer's own equity, cap price	$ 56.75
Q1 2014 [Member]
Shares received upon settlement of capped call	0.6
Economic value of shares received upon settlement of capped call	38,000,000
Q4 2014 [Member]
Shares received upon settlement of capped call	1.5
Economic value of shares received upon settlement of capped call	$ 102,000,000