Compensation Plans Stock Option Grants Under the Equity Incentive Compensation Plan (Details) - USD ($)	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Compensation plans
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Stock Options	$ 0	$ 0
Proceeds from Stock Options Exercised		4,000,000	$ 3,200,000
Employee Service Share-based Compensation, Tax Benefit Realized from Exercise of Stock Options	$ 0	$ 0	$ 0
Shares
Outstanding, start of year	0	39,088	267,846
Exercised		(39,088)	(228,758)
Forfeited		0	0
Outstanding, end of year		0	39,088
Vested and exercisable at end of year		0	39,088
Weighted Average Exercise Price
Outstanding, start of year (in dollars per share)	$ 0.00	$ 20.87	$ 14.95
Exercised (in dollars per share)		20.87	13.92
Forfeited (in dollars per share)		0	0
Outstanding, end of year (in dollars per share)		0.00	20.87
Vested and exercisable at end of year (in dollars per share)		$ 0.00	$ 20.87
Aggregate Intrinsic Value
Exercised		$ 1,993,726	$ 12,326,994
Outstanding		0	2,432,837
Vested and exercisable at end of year		$ 0	$ 2,432,837
Employee Stock Option [Member]
Compensation plans
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years

Share-based Compensation Arrangement by Share-based Payment Award, Options, Total Intrinsic Value [Abstract]

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- Definition

Unrecognized cost of unvested options awarded to employees as compensation.

+ References

No definition available.

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- Definition

Disclosure of the aggregate tax benefit realized from the exercise of stock options and the conversion of similar instruments during the annual period.

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- Definition

The cash inflow associated with the amount received from holders exercising their stock options. This item inherently excludes any excess tax benefit, which the entity may have realized and reported separately.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (j)
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
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-Section 45
-Paragraph 14
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-Publisher FASB
-Name Accounting Standards Codification
-Glossary Financing Activities
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

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.

+ References

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

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

+ References

No definition available.

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- Definition

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

+ References

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- References

No definition available.

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- Definition

The number of exercisable share options (fully vested and expected to vest) that may be converted as of the balance sheet date.

+ References

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As of the balance sheet date, the weighted-average exercise price (at which grantees can acquire the shares reserved for issuance) for exercisable stock options that are fully vested or expected to vest.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of fully vested and expected to vest options outstanding.

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- Definition

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

+ References

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- Definition

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

+ References

No definition available.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-Publisher SEC
-Name Regulation S-X (SX)
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-Section 02
-Paragraph 29, 30
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