Commitments and contingencies (Narrative) (Details)								1 Months Ended																							3 Months Ended		12 Months Ended
	Jul. 12, 2018 USD ($) T	Jun. 10, 2017 USD ($)	Jun. 10, 2017 CNY (¥)	Jun. 09, 2017 USD ($)	Jun. 09, 2017 CNY (¥)	Sep. 06, 2016 USD ($)	Sep. 06, 2016 CNY (¥)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 CNY (¥)	Jun. 25, 2018 USD ($) T	Jun. 25, 2018 CNY (¥) T	Jun. 25, 2018 T	Mar. 31, 2018 USD ($)	Mar. 31, 2018 CNY (¥)	Jul. 21, 2017 T	Mar. 31, 2017 USD ($)	Mar. 31, 2017 CNY (¥)	Mar. 30, 2017 USD ($)	Mar. 30, 2017 CNY (¥)	Mar. 17, 2017 USD ($) T	Feb. 20, 2017 USD ($)	Feb. 20, 2017 CNY (¥)	Nov. 15, 2016 USD ($)	Nov. 15, 2016 CNY (¥)	Oct. 20, 2016 USD ($)	Oct. 20, 2016 CNY (¥)	Apr. 30, 2015 USD ($)	Apr. 30, 2015 AED (د.إ)	Mar. 31, 2013 USD ($)	Mar. 31, 2013 CNY (¥)	Mar. 31, 2019 USD ($) T	Mar. 31, 2019 CNY (¥) T	Dec. 31, 2017 USD ($)	Dec. 31, 2017 CNY (¥)	Mar. 31, 2019 CNY (¥)	Mar. 31, 2019 AED (د.إ)	Dec. 31, 2018 USD ($)	Jul. 12, 2018 CNY (¥)	Jun. 21, 2018 USD ($)	Jun. 21, 2018 CNY (¥)	Dec. 31, 2017 CNY (¥)	Mar. 17, 2017 CNY (¥)	Nov. 15, 2016 CNY (¥)	Sep. 06, 2016 CNY (¥)
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers																															$ 524,297,914						$ 530,636,319
Xinda Holdings HK [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation																															8,100,000
Xinda Holdings HK [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation | ¥																																			¥ 54,800,000
Xinda Holdings HK [Member] | Property, Plant and Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																													$ 267,300,000
Xinda Holdings HK [Member] | Property, Plant and Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																														¥ 1,800,000,000
Xinda Holdings HK [Member] | Working Capital [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																													$ 89,100,000
Xinda Holdings HK [Member] | Working Capital [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																														¥ 600,000,000
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] | 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] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration						$ 2,500,000																									255,900,000
Purchase Obligation						$ 200,000																									1,400,000
Prepayments to equipment suppliers																							$ 18,000,000								900,000								$ 254,000,000
Bio-composite material | T																				300,000
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] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥							¥ 17,000,000																									¥ 1,722,900,000
Purchase Obligation | ¥																																			9,400,000									¥ 1,600,000
Prepayments to equipment suppliers | ¥																																			6,000,000					¥ 1,710,000,000			¥ 120,900,000
Sichuan Xinda [Member] | Equipment [Member] | China, Yuan Renminbi [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers | ¥																																											¥ 74,000,000
Peaceful [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																									$ 13,300,000						8,300,000
Prepayments to equipment suppliers																															5,000,000
Peaceful [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																										¥ 89,800,000						55,900,000
Prepayments to equipment suppliers | ¥																																			33,900,000
Beijin Construction [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers																															7,006,972						6,867,269
Beijin Construction [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration		$ 3,500,000																			$ 400,000		$ 35,400,000
Purchase Obligation																															21,300,000
Beijin Construction [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥			¥ 23,800,000																			¥ 2,900,000		¥ 237,600,000
Purchase Obligation | ¥																																			143,400,000
Hailezi [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to equipment suppliers																															511,758,267						$ 502,087,116
Prepayments to be refunded from termination of contracts																																	$ 1,800,000
Refunded amount in agreement																																	54,800,000
Hailezi [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Prepayments to be refunded from termination of contracts | ¥																																		¥ 12,400,000
Refunded amount in agreement | ¥																																									¥ 369,100,000
Hailezi [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																$ 333,100,000
Prepayments to equipment suppliers																																	$ 92,300,000
Prepayments to be refunded from termination of contracts								$ 253,200,000					$ 253,200,000
Hailezi [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																	¥ 2,242,800,000
Prepayments to equipment suppliers | ¥																																									¥ 621,600,000
Prepayments to be refunded from termination of contracts | ¥									¥ 1,704,900,000					¥ 1,704,900,000
Hailezi [Member] | Warehouse Construction Contract [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation																															4,600,000
Hailezi [Member] | Warehouse Construction Contract [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation | ¥																																			31,200,000
Harbin Hailezi Science and Technology Co. Ltd. ("Hailezi") [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																															330,100,000
Purchase Obligation																															300,000
Prepayments to equipment suppliers																															2,700,000
Harbin Hailezi Science and Technology Co. Ltd. ("Hailezi") [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																																2,222,900,000
Purchase Obligation | ¥																																			1,900,000
Prepayments to equipment suppliers | ¥																																			18,000,000
Nanchong Project [Member] | Property, Plant and Equipment [Member]
Long-term Purchase Commitment [Line Items]
Bio-composite material | T																				20,000
Refunded amount in agreement																				$ 253,200,000
Nanchong Project [Member] | Property, Plant and Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Refunded amount in agreement | ¥																																										¥ 1,704,900,000
Nanchong Project [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																															282,300,000
Purchase Obligation																															28,300,000
Prepayments to equipment suppliers																															254,000,000
Nanchong Project [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																																1,900,000,000
Purchase Obligation | ¥																																			190,000,000
Prepayments to equipment suppliers | ¥																																			1,710,000,000
HLJ Project [Member]
Long-term Purchase Commitment [Line Items]
Total capital expenditure																															596,300,000
Investment in fixed assets																															489,300,000
HLJ Project [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total capital expenditure | ¥																																4,015,000,000
Investment in fixed assets | ¥																																¥ 3,295,000,000
HLJ Project [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation																															66,800,000
Prepayments to equipment suppliers	$ 35,800,000																														44,600,000
HLJ Project [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation | ¥																																			449,100,000
Prepayments to equipment suppliers | ¥																																			300,700,000			¥ 240,800,000
HLJ Xinda Group [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation																															2,800,000
HLJ Xinda Group [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation | ¥																																			18,800,000
HLJ Xinda Group [Member] | Property, Plant and Equipment [Member]
Long-term Purchase Commitment [Line Items]
Bio-composite material | T															100,000
HLJ Xinda Group [Member] | Equipment [Member]
Long-term Purchase Commitment [Line Items]
Total consideration										$ 111,400,000																					$ 136,000,000
Prepayments to equipment suppliers	$ 171,800,000																																						$ 136,800,000
Bio-composite material | T	300,000									300,000	300,000	300,000			300,000																300,000	300,000
HLJ Xinda Group [Member] | Equipment [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥											¥ 749,800,000																					¥ 916,200,000
Prepayments to equipment suppliers | ¥																																			920,900,000			¥ 1,157,000,000
Falcon Red Eye Contracting Co LLC [Member] | Warehouse Construction Contract [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																											$ 1,800,000
Purchase Obligation																															$ 400,000
Falcon Red Eye Contracting Co LLC [Member] | Warehouse Construction Contract [Member] | United Arab Emirates, Dirhams
Long-term Purchase Commitment [Line Items]
Total consideration | د.إ																												د.إ 6,700,000
Purchase Obligation | د.إ																																				د.إ 1,600,000
Beijing Fangyuan Decoration Engineering Co [Member] | Workshops and buildings [Member]
Long-term Purchase Commitment [Line Items]
Total consideration				$ 200,000														$ 900,000
Purchase Obligation																															600,000
Beijing Fangyuan Decoration Engineering Co [Member] | Workshops and buildings [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																															300,000
Beijing Fangyuan Decoration Engineering Co [Member] | Workshops and buildings [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥					¥ 1,200,000														¥ 5,800,000
Purchase Obligation | ¥																																			3,800,000
Beijing Fangyuan Decoration Engineering Co [Member] | Workshops and buildings [Member] | China, Yuan Renminbi [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																																2,000,000
Beijing Zhonghongwufang Stone Co [Member] | Workshops and buildings [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation																															100,000
Beijing Zhonghongwufang Stone Co [Member] | Workshops and buildings [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Total consideration																															$ 100,000
Beijing Zhonghongwufang Stone Co [Member] | Workshops and buildings [Member] | China, Yuan Renminbi [Member]
Long-term Purchase Commitment [Line Items]
Purchase Obligation | ¥																																			¥ 600,000
Beijing Zhonghongwufang Stone Co [Member] | Workshops and buildings [Member] | China, Yuan Renminbi [Member] | Construction in progress [Member]
Long-term Purchase Commitment [Line Items]
Total consideration | ¥																																¥ 600,000