Equity Incentive Awards - Stock option activity (Details) - $ / shares		12 Months Ended
May 10, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares Subject To Options
Beginning balance (in shares)		865,600	1,085,600
Options issued (in shares)	7,550	7,550
Options exercised (in shares)		(440,000)	(220,000)	0
Ending balance (in shares)		433,150	865,600	1,085,600
Exercisable at December 31, 2016 (in shares)		427,836
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Beginning balance (in usd per share)		$ 23.12	$ 21.95
Options issued (in usd per share)	$ 74.53	74.53
Options exercised (in usd per share)		25.66	17.35
Ending balance (in usd per share)		21.44	$ 23.12	$ 21.95
Exercisable at December 31, 2016 (in usd per share)		$ 20.79
Weighted Average Outstanding Contractual Life (in years)		1 year 8 months	1 year 7 months	2 years 1 month 1 day
Exercisable at December 31, 2016 (in years)		1 year 7 months

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

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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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-Publisher FASB
-Name Accounting Standards Codification
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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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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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

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