Shareholders' Equity (Details) (USD $) In Thousands, except Share data in Millions, unless otherwise specified	3 Months Ended									12 Months Ended	3 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Mar. 31, 2015
Shareholders' Equity
Current quarter dividend declared and paid (in dollars per share)			$ 0.25	$ 0.25			$ 0.12	$ 0.12
Common Stock, Dividend Declared Prior Quarter Paid Current Quarter (in dollars per share)	$ 0.30			$ 0.25	$ 0.25			$ 0.12
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 in current period	$ 236,100									$ 236,074
Document Fiscal Year Focus										2014
Common stock dividends declared (in dollars per share)	$ 0.30	$ 0.30	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.12	$ 0.12	$ 0.12
Subsequent event
Shareholders' Equity
Common Stock, Dividend Declared Prior Quarter Paid Current Quarter (in dollars per share)											$ 0.30