Common Stock (Schedule of Stock Option Activity) (Details) - $ / shares shares in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares
Outstanding at beginning of period (in shares)	561	652	875
Granted (in shares)	0	0	0
Exercised (shares)	(54)	(87)	(213)
Canceled (in shares)	0	(4)	(10)
Outstanding at end of period (in shares)	507	561	652
Exercisable (in shares)	507	537	564
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 20.99	$ 19.99	$ 17.85
Granted (in dollars per share)	0.00	0.00	0.00
Exercised (in dollars per share)	17.42	13.54	11.21
Canceled (in dollars per share)	0.00	20.29	19.98
Outstanding at end of period (in dollars per share)	21.37	20.99	19.99
Exercisable (in dollars per share)	$ 21.37	$ 19.49	$ 16.18

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iii)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.

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- Definition

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

+ References

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-SubTopic 10
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-Subparagraph (c)(1)(iv)(3)-(4)
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Weighted average price of options that were either forfeited or expired.

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-Name Accounting Standards Codification
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-SubTopic 10
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Gross number of share options (or share units) granted during the period.

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Number of options outstanding, including both vested and non-vested options.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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Number of share options (or share units) exercised during the current period.

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