Restatement and Revision of Prior Period Financial Statements - Condensed Consolidated Statements of Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)	$ (738)	$ 7,116	$ 4,374	$ 5,678	$ 4,765	$ 4,225	$ (1,905)	$ (3,136)	$ 10,052	$ (5,043)	$ 17,168	$ (817)	$ 16,430	$ 3,949	$ (32,389)
Comprehensive income (loss)		9,284	8,253	7,657		4,024	(3,295)	(3,411)	15,911	(6,708)	25,196	(2,683)	18,150	(3,198)	(40,640)
As Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)	1,500	7,528	4,493	5,456	5,047	4,341	(2,324)	(2,693)	9,951	(5,017)	17,479	(676)	18,979	4,370	(33,063)
Comprehensive income (loss)		9,696	8,373	7,435		4,140	(3,714)	(3,163)	15,810	(6,877)	25,506	(2,201)	20,697	(2,436)	(41,655)
Adjustments
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net income (loss)	$ (2,238)	(411)	(120)	222	$ (282)	(116)	419	(443)	101	(26)	(311)	(141)	(2,549)	(421)	674
Comprehensive income (loss)		$ (411)	$ (120)	$ 222		$ (116)	$ 419	$ (248)	$ 101	$ 169	$ (311)	$ (482)	$ (2,547)	$ (762)	$ 1,015