Shareholders' Equity (Details) (USD $) In Thousands, except Share data in Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shareholders' Equity
Cash dividend declared	$ 108,630us-gaap_DividendsCommonStockCash	$ 97,375us-gaap_DividendsCommonStockCash	$ 87,698us-gaap_DividendsCommonStockCash
Dividends declared per share (in dollars per share)	$ 0.46	$ 0.44	$ 0.40
Cash dividend paid	$ 105,379us-gaap_PaymentsOfDividendsCommonStock	$ 94,812us-gaap_PaymentsOfDividendsCommonStock	$ 87,633us-gaap_PaymentsOfDividendsCommonStock
Treasury Stock
Remaining authorization to repurchase treasury stock (in shares)	3.6

Aggregate dividends declared during the period for each share of common stock outstanding.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

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- Definition

Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

+ References

+ Details

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- Details

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Data Type:	xbrli:stringItemType
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- Definition

Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3291-108585

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- Definition

The remaining number of shares authorized to be repurchased by an entity's Board of Directors under a stock repurchase plan.

+ References

No definition available.

+ Details

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