Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($)
Statement of Stockholders' Equity [Abstract]
Expense related to distribution or servicing and underwriting fees	$ 1,345

Expense related to distribution, servicing and underwriting fees.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.14)
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Name:	us-gaap_ExpenseRelatedToDistributionOrServicingAndUnderwritingFees
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration