Shareholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions	1 Months Ended		3 Months Ended										12 Months Ended
	Feb. 18, 2016	Oct. 23, 2015	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2015	Dec. 31, 2014	Oct. 01, 2015
Shareholders' Equity
Common Stock, Dividend Declared Prior Quarter Paid Current Quarter (in dollars per share)				$ 0.375			$ 0.30	$ 0.30			$ 0.25
Treasury stock, shares acquired								3.5
Treasury stock acquired, price per share								$ 67.45
Number of shares sold to a third party investor by the shareholder														3.5
Total cost of treasury stock, acquired during the period													$ 200,000	$ 236,074
Document Fiscal Year Focus													2014
Common Stock Dividend Declared And Paid During The Same Period						$ 0.30	0.30			$ 0.25	0.25
Common stock dividends declared (in dollars per share)				$ 0.375	$ 0.375	$ 0.3	$ 0.3	$ 0.3	$ 0.3	$ 0.25	$ 0.25	$ 0.25
October 2015 Stock Repurchase
Shareholders' Equity
Stock Repurchase Program, Authorized Amount															$ 500,000
Accelerated stock repurchase agreement October 23, 2015 | October 2015 Stock Repurchase
Shareholders' Equity
Stock Repurchase Program, Authorized Amount															$ 200,000
Accelerated Share Repurchases, Settlement (Payment) or Receipt		$ 200,000
Treasury stock, shares acquired		1.6
Accelerated stock repurchase agreement October 23, 2015 | November 2015 Stock Repurchase
Shareholders' Equity
Treasury stock, shares acquired				0.5
Accelerated stock repurchase agreement October 23, 2015 | Total stock repurchased during the period
Shareholders' Equity
Treasury stock, shares acquired				2.1
Treasury stock acquired, price per share				$ 95.09
Subsequent event
Shareholders' Equity
Common Stock, Dividend Declared Prior Quarter Paid Current Quarter (in dollars per share)			$ 0.375
Subsequent event | October 2015 Stock Repurchase
Shareholders' Equity
Treasury stock, shares acquired	2.1
Total cost of treasury stock, acquired during the period	$ 150,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 150,000