Stockholders' Equity (Schedule of Stock Options) (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Number of Option Shares
Exercised (in shares)	(274,177)	(239,854)	(395,274)
Equity Plan
Number of Option Shares
Balance at beginning of the period (in shares)	26,880	212,030
Exercised (in shares)	(26,180)	(183,600)
Forfeited (in shares)	(700)	(1,550)
Balance at end of the period (in shares)	0	26,880	212,030
Option exercisable (in shares)	0
Weighted Average Exercise Price
Balance at beginning of the period (in usd per share)	$ 17.17	$ 15.38
Exercised (in usd per share)	17.17	15.10
Forfeited (in usd per share)	17.17	17.17
Balance at end of the period (in usd per share)	0	$ 17.17	$ 15.38
Options exercisable (in usd per share)	$ 0

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.

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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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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.

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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 price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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

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