Lines of credit (Details) - USD ($)		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Line of Credit Facility [Line Items]
Maximum Amount Available of Line of Credit		$ 102,581,700	$ 79,774,838
Unused line of credit		$ 23,826,843	$ 31,273,785
Bank of China [Member]
Line of Credit Facility [Line Items]
Starting date	[1]	Oct. 30, 2018	Jul. 11, 2016
Maturity date	[1]	Oct. 30, 2021	Jul. 11, 2019
Maximum Amount Available of Line of Credit	[1]	$ 12,777,080	$ 13,445,197
Unused line of credit	[1]	$ 389,445	$ 8,279,168
Bank of China [Member]
Line of Credit Facility [Line Items]
Starting date	[1]	Sep. 03, 2018	Jul. 12, 2016
Maturity date	[1]	Sep. 03, 2019	Jul. 12, 2019
Maximum Amount Available of Line of Credit	[1]	$ 29,691,501	$ 12,292,752
Unused line of credit	[1]	$ 4,643,021	$ 3,366,677
Industrial and Commercial Bank of China
Line of Credit Facility [Line Items]
Starting date	[1]	Aug. 28, 2018	Aug. 24, 2017
Maturity date	[1]	Aug. 28, 2019	Aug. 31, 2018
Maximum Amount Available of Line of Credit	[1]	$ 7,301,188	$ 7,682,970
Unused line of credit	[1]	$ 744,721	$ 6,146,376
China Everbright Bank [Member]
Line of Credit Facility [Line Items]
Starting date	[2]	Jan. 24, 2018
Maturity date	[2]	Jan. 23, 2019
Maximum Amount Available of Line of Credit	[2]	$ 7,301,188
Unused line of credit	[2]	$ 0
Industrial Bank Co., Ltd.
Line of Credit Facility [Line Items]
Starting date	[1]	Mar. 15, 2018	Sep. 20, 2017
Maturity date	[1]	Mar. 15, 2019	Sep. 20, 2018
Maximum Amount Available of Line of Credit	[1]	$ 5,840,951	$ 3,073,188
Unused line of credit	[1]	$ 364,446	$ 517,832
Guangdong Huaxing Bank
Line of Credit Facility [Line Items]
Starting date	[1]	Sep. 13, 2018	Oct. 26, 2017
Maturity date	[1]	Aug. 07, 2019	Sep. 27, 2018
Maximum Amount Available of Line of Credit	[1]	$ 23,363,804	$ 9,219,564
Unused line of credit	[1]	$ 10,829,780	$ 3,543,386
Ping An Bank Co., Ltd.
Line of Credit Facility [Line Items]
Starting date	[1]	May 15, 2018	Mar. 17, 2017
Maturity date	[1]	May 14, 2019	Mar. 16, 2018
Maximum Amount Available of Line of Credit	[1]	$ 10,221,664	$ 10,756,158
Unused line of credit	[1]	$ 6,851,536	$ 3,130,042
Jiang Su Bank Co., Ltd.
Line of Credit Facility [Line Items]
Starting date	[1]	Sep. 25, 2018	Apr. 20, 2017
Maturity date	[1]	Sep. 24, 2019	Apr. 19, 2018
Maximum Amount Available of Line of Credit	[1]	$ 6,084,324	$ 3,841,485
Unused line of credit	[1]	$ 3,894	$ 113,708
China Minsheng Banking Corp., Ltd.
Line of Credit Facility [Line Items]
Starting date	[1]		Nov. 14, 2017
Maturity date	[1]		Nov. 14, 2018
Maximum Amount Available of Line of Credit	[1]		$ 5,121,980
Unused line of credit	[1]		$ 1,280,495
Hua Xia Bank Co., Ltd.
Line of Credit Facility [Line Items]
Starting date	[2]		Oct. 23, 2017
Maturity date	[2]		Oct. 23, 2018
Maximum Amount Available of Line of Credit	[2]		$ 7,682,970
Unused line of credit	[2]		$ 4,745,002
Bank of China
Line of Credit Facility [Line Items]
Starting date	[1]		Jul. 25, 2016
Maturity date	[1]		Jul. 25, 2019
Maximum Amount Available of Line of Credit	[1]		$ 4,097,584
Unused line of credit	[1]		$ 143,928
Jiang Su Bank Co., Ltd.
Line of Credit Facility [Line Items]
Starting date	[2]		Jul. 03, 2017
Maturity date	[2]		Jul. 02, 2018
Maximum Amount Available of Line of Credit	[2]		$ 2,560,990
Unused line of credit	[2]		$ 7,171

[1] The lines of credits are guaranteed by the Company’s Chief Executive Officer, Mr. Dang Yu Pan.

[2] The lines of credits are guaranteed by the Company’s Chief Executive Officer, Mr. Dang Yu Pan, and his wife.