Indebtedness (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Indebtedness
Long-term debt	$ 94,729	$ 189,605
Senior 5.0% unsecured notes due, 2018 ("Series A Notes")
Indebtedness
Fair value of outstanding indebtedness	97,000
Long-term debt	94,900
Senior 5.75% unsecured notes due, 2021 ("Series B Notes")
Indebtedness
Fair value of outstanding indebtedness	103,000
Long-term debt	$ 94,700

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Name:	us-gaap_LongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant