Long-term debt: Senior unsecured notes- $200.0 million 2021 Notes (Details) - USD ($) $ in Millions		12 Months Ended
Apr. 09, 2014	Dec. 31, 2015
Senior Unsecured Notes
Senior unsecured notes- $200.0 million 2021 Notes
Aggregate principal amount of debt issued		$ 200.0
Percentage of principal amount at which notes will be required to be repurchased in the event of a change of control		101.00%
Senior Unsecured Notes \| Treasury Rate
Senior unsecured notes- $200.0 million 2021 Notes
Discount rate used to compute make-whole premium, basis points added to reference rate (as a percent)		0.50%
Senior Unsecured Notes \| Prior to April 15, 2017
Senior unsecured notes- $200.0 million 2021 Notes
Percentage of principal amount that the holders of the Convertible Notes may require the Company to repurchase		100.00%
Percentage of redemption price which may redeem with net cash proceeds from certain equity offerings		105.625%
Percentage of redemption price of principal amount accrued interest		104.219%
Percentage of outstanding principal amount used in calculation of make-whole premium		1.00%
Maximum percentage of principal amount of debt instrument which the entity could redeem with proceeds from certain equity offerings		35.00%
Senior Unsecured Notes \| 12-month period beginning on April 15, 2017
Senior unsecured notes- $200.0 million 2021 Notes
Percentage of principal amount that the holders of the Convertible Notes may require the Company to repurchase		104.219%
Senior Unsecured Notes \| 12-month period beginning on April 15, 2018
Senior unsecured notes- $200.0 million 2021 Notes
Percentage of principal amount that the holders of the Convertible Notes may require the Company to repurchase		102.813%
Senior Unsecured Notes \| 12-month period beginning on April 15, 2019
Senior unsecured notes- $200.0 million 2021 Notes
Percentage of principal amount that the holders of the Convertible Notes may require the Company to repurchase		101.406%
Senior Unsecured Notes \| 12-month period beginning on April 15, 2020
Senior unsecured notes- $200.0 million 2021 Notes
Percentage of principal amount that the holders of the Convertible Notes may require the Company to repurchase		100.00%
Senior Unsecured Notes \| Cogent Finance
Senior unsecured notes- $200.0 million 2021 Notes
Aggregate principal amount of debt issued	$ 200.0
Interest rate (as a percent)	5.625%
Proceeds from issuance of long-term debt, net of issuance costs	$ 195.8
Senior Secured Notes
Senior unsecured notes- $200.0 million 2021 Notes
Aggregate principal amount of debt issued		$ 240.0

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Represents the redemption price as a percentage of the principal amount at which the debt instrument is required to be redeemed in the event of a change of control.

+ References

No definition available.

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Represents the percentage of redemption price of principal amount accrued interest.

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Represents the percentage price of original principal amount of debt instrument that the entity may redeem with net cash proceeds from certain equity offerings.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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Face (par) amount of debt instrument at time of issuance.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Contractual interest rate for funds borrowed, under the debt agreement.

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Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

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