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Discount rate from fair value on purchase date that participants pay for shares.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Equity Compensation Plans (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total intrinsic value of options exercised		$ 5,121	$ 3,550	$ 2,740
Tax benefit recognized		0	0	0
Share-based compensation expense recognized		14,615	11,697	8,997
Unrecognized compensation costs related to non-vested share-based compensation arrangements with performance shares		23,331
Share-based compensation expense		$ 14,615	11,697	8,997
Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost		2 years 2 months 12 days
Stock options compensation costs		$ 2,197
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period of recognizing cost		2 years 2 months 12 days
Total fair value of restricted stock vested		$ 6,235	$ 5,102	2,767
Unrecognized compensation costs related to non-vested performance options		$ 21,134
Performance options awarded to President and CEO		771	710
Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiry of options from the date of grant		10 years
Share-based compensation expense		$ 43	$ 269	546
Performance options awarded to President and CEO	450
Number of shares options vest in		25
Period of considering closing price of common stock		30 days
Contractual term (years)		10 years
Stock Options And Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized		$ 13,908	$ 10,872	$ 8,072
Minimum [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)		5 years 2 months 16 days	5 years 3 months 7 days	5 years 2 months 12 days
Expected volatility of stock		43.00%	46.00%	46.00%
Interest rate		1.75%	1.06%	1.30%
Minimum [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price		$ 5.91
Expected volatility of stock		60.50%
Interest rate		1.75%
Maximum [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual term (years)		5 years 9 months 4 days	7 years 1 month 6 days	6 years 10 months 21 days
Expected volatility of stock		48.00%	51.00%	67.00%
Interest rate		2.12%	2.02%	1.96%
Maximum [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Strike price		$ 21.04
Expected volatility of stock		69.60%
Interest rate		2.73%
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiry of options from the date of grant		10 years
Common stock reserved for issuance		10,249
Shares available for future grants		1,128
2014 Plan [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercisable period beginning		3 years
2014 Plan [Member] \| Minimum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		1 year
2014 Plan [Member] \| Maximum [Member] \| Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
2008 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense recognized		$ 664	$ 556	$ 379
Company's common stock may be purchased at a discount		15.00%
Participants purchase limit value		$ 25
Description of participants purchase limit		Participants may not purchase more than $25 of the Company's common stock in a calendar year and may not purchase a value of more than 3 shares during an offering period.
Participants purchase limit shares		3
Offering period		6 months
Shares available for sale under the ESPP increased		2.00%
Outstanding shares of common stock exceed		600
Shares available for future issuance under the ESPP		225
First Anniversary Date Of Grant [Member] \| 2014 Plan [Member] \| Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual vesting percentage		25.00%
Tranche 4 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		$ 17.50
Tranche 5 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		20.00
Tranche 6 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		25.00
Tranche 7 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		30.00
Tranche 8 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		35.00
Tranche 9 [Member] \| Performance Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price by which volume adjusted weighted average closing price exceeds under vesting condition		$ 40.00