Prepayments to equipment and construction suppliers (Narrative) (Details)				1 Months Ended										3 Months Ended		12 Months Ended
		Jul. 12, 2018 USD ($) T	Jul. 12, 2018 CNY (¥) T	Jun. 30, 2018 USD ($)	Jun. 30, 2018 CNY (¥)	Jun. 25, 2018 T	Jun. 25, 2018 T	Mar. 31, 2018 USD ($)	Mar. 31, 2018 CNY (¥)	Dec. 31, 2017 USD ($) a	Jul. 21, 2017 a T	Mar. 17, 2017 USD ($) a T	Mar. 17, 2017 CNY (¥) a T	Mar. 31, 2019 USD ($) T	Mar. 31, 2019 CNY (¥) T	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CNY (¥)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 CNY (¥)	Mar. 31, 2019 CNY (¥)	Dec. 31, 2018 USD ($)	Nov. 30, 2018 USD ($)	Nov. 30, 2018 CNY (¥)	Jul. 12, 2018 CNY (¥)	Jun. 21, 2018 USD ($)	Jun. 21, 2018 CNY (¥)	Dec. 31, 2017 CNY (¥)	Sep. 10, 2017 USD ($)	Sep. 10, 2017 CNY (¥)	Mar. 17, 2017 CNY (¥)	Feb. 20, 2017 USD ($)	Feb. 20, 2017 CNY (¥)	Nov. 15, 2016 USD ($)	Nov. 15, 2016 CNY (¥)	Oct. 20, 2016 USD ($)	Oct. 20, 2016 CNY (¥)
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers														$ 524,297,914							$ 530,636,319
Receivable, Related Parties	[1]													7,425,559							7,285,231
Sichuan Xinda [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers														18,000,000
Sichuan Xinda [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers														11,000,000
Sichuan Xinda [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Bio-composite material | T												300,000	300,000
Prepayments to equipment suppliers														900,000											$ 254,000,000								$ 18,000,000
Total consideration										$ 116,200,000						$ 116,200,000									282,300,000			$ 3,500,000			$ 400,000		35,400,000
Prepaid												$ 256,800,000
Sichuan Xinda [Member] | Equipment [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers																																	$ 11,000,000
Sichuan Xinda [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				¥ 120,900,000
Sichuan Xinda [Member] | China, Yuan Renminbi [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				74,000,000
Sichuan Xinda [Member] | China, Yuan Renminbi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				6,000,000						¥ 1,710,000,000								¥ 120,900,000
Total consideration | ¥																										1,900,000,000	¥ 782,200,000		¥ 23,800,000			¥ 2,900,000		237,600,000
Prepaid | ¥													¥ 1,728,900,000
Sichuan Xinda [Member] | China, Yuan Renminbi [Member] | Equipment [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																																		¥ 74,000,000
Hailezi [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers														511,758,267							$ 502,087,116
Total consideration										42,100,000						42,100,000
Prepayments to be refunded from termination of contracts																1,800,000
Refunded amount in agreement										54,800,000						54,800,000
Refund of prepayment														3,100,000
Receivable, Related Parties																						$ 500,000
Hailezi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers										92,300,000						92,300,000
Prepayments to be refunded from termination of contracts				$ 253,200,000				$ 253,200,000
Hailezi [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																											283,700,000
Prepayments to be refunded from termination of contracts | ¥																	¥ 12,400,000
Refunded amount in agreement | ¥																											369,100,000
Refund of prepayment | ¥															¥ 20,800,000
Receivable, Related Parties | ¥																							¥ 3,200,000
Hailezi [Member] | China, Yuan Renminbi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																											621,600,000
Prepayments to be refunded from termination of contracts | ¥					¥ 1,704,900,000				¥ 1,704,900,000
Nanchong Project [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers														254,000,000
Nanchong Project [Member] | Property, Plant and Equipment [Member]
Long-term Purchase Commitment [Line Items]
Bio-composite material | T												20,000	20,000
Area of property | a												41.2	41.2
Net capital expenditures												$ 371,300,000
Refunded amount in agreement												253,200,000
Remaining amount of prepaid prepayments												$ 3,600,000
Nanchong Project [Member] | China, Yuan Renminbi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				1,710,000,000
Nanchong Project [Member] | China, Yuan Renminbi [Member] | Property, Plant and Equipment [Member]
Long-term Purchase Commitment [Line Items]
Net capital expenditures | ¥																														¥ 2,500,000,000
Refunded amount in agreement | ¥																														1,704,900,000
Remaining amount of prepaid prepayments | ¥																														¥ 24,000,000
Peaceful [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers														5,000,000
Total consideration																																			$ 13,300,000
Peaceful [Member] | China, Yuan Renminbi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				33,900,000
Total consideration | ¥																																				¥ 89,800,000
HLJ Xinda Group [Member]
Long-term Purchase Commitment [Line Items]
Prepaid														$ 37,500,000
HLJ Xinda Group [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Bio-composite material | T		300,000	300,000			300,000	300,000				300,000			300,000	300,000
Prepayments to equipment suppliers		$ 171,800,000																							136,800,000
Total consideration		171,800,000												$ 139,600,000											$ 749,800,000
Prepaid		$ 35,800,000												44,600,000
HLJ Xinda Group [Member] | Property, Plant and Equipment [Member]
Long-term Purchase Commitment [Line Items]
Bio-composite material | T											100,000
Area of property | a											41.2
HLJ Xinda Group [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Prepaid | ¥															¥ 252,500,000
HLJ Xinda Group [Member] | China, Yuan Renminbi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				920,900,000				¥ 1,157,000,000
Total consideration | ¥																				939,700,000				¥ 1,157,000,000		¥ 111,400,000
Prepaid | ¥			¥ 240,800,000												¥ 300,700,000
Green River [Member] | Workshops and buildings [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers										$ 16,100,000				$ 16,100,000		16,100,000
Area of property | a										13,972.64
Total consideration										$ 32,200,000						$ 32,200,000
Green River [Member] | Workshops and buildings [Member] | Subsequent Event [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers																		$ 16,100,000
Green River [Member] | China, Yuan Renminbi [Member] | Workshops and buildings [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																				¥ 108,300,000							108,300,000
Total consideration | ¥																											¥ 216,600,000
Green River [Member] | China, Yuan Renminbi [Member] | Workshops and buildings [Member] | Subsequent Event [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																			¥ 108,300,000

[1] On December 18, 2018, HLJ Xinda Group entered into an agreement with Mr. Xiaohui Gao, General Manager of Heilongjiang Xinda Enterprise Group Shanghai New Materials Sales Company Limited ("Shanghai Sales"), to transfer the wholly owned equity from HLJ Xinda Group to Mr. Gao for a total consideration of RMB50.0 million (equivalent to US$7.4 million). Pursuant to the contract, the Company completed the legal transfer on December 19, 2018 and the full consideration of $7.4 million was received on April 11, 2019.