Contractual interest rate for funds borrowed, under the debt agreement.

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

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical)	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
2 3/4 Percent Convertible Senior Notes [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Interest rate on convertible senior notes	2.75%	2.75%	2.75%	2.75%
1 Percent Convertible Senior Notes [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Interest rate on convertible senior notes	1.00%	1.00%	1.00%	1.00%