Additional paid-in capital (Details Textual) (USD $)	1 Months Ended	12 Months Ended				0 Months Ended
	May 27, 2014	Dec. 31, 2014		Dec. 31, 2013		Sep. 16, 2014	Aug. 13, 2013	Aug. 11, 2014	Oct. 13, 2014	Sep. 30, 2014	Sep. 26, 2014
Additional Paid In Capital [Line Items]
Common Stock, Dividends, Per Share, Declared	$ 0.18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross		22,500		22,500
Business Acquisition Cost Of Non Controlling Interest										$ 34,500,000
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		7,502,000	[1]	0	[1]
Director [Member]
Additional Paid In Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross						22,500	22,500
Noncontrolling Interest [Member]
Additional Paid In Capital [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		29,812,000		0
Henglong [Member]
Additional Paid In Capital [Line Items]
Equity Method Investment, Ownership Percentage										100.00%	20.00%
Henglong [Member] | Private Placement [Member]
Additional Paid In Capital [Line Items]
Stock Issued During Period, Shares, Acquisitions								3,260,000
Equity Method Investment, Ownership Percentage								20.00%
Jiulong [Member]
Additional Paid In Capital [Line Items]
Equity Method Investment, Ownership Percentage										100.00%	19.00%
Jiulong [Member] | Private Placement [Member]
Additional Paid In Capital [Line Items]
Stock Issued During Period, Shares, Acquisitions								818,000
Equity Method Investment, Ownership Percentage								19.00%
Henglong and Jiulong [Member]
Additional Paid In Capital [Line Items]
Business Acquisition Cost Of Non Controlling Interest		34,500,000
Stock Issued During Period, Value, Acquisitions								37,300,000
Sale of Stock, Price Per Share								9.15
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Adjustment, before Tax, Portion Attributable to Noncontrolling Interest		4,700,000
Business Combination Consideration Transferred Equity Interests Issued									4,078,000
Redeemable Noncontrolling Interest, Equity, Common, Fair Value		37,300,000
Redeemable Noncontrolling Interest, Equity, Common, Carrying Amount		34,500,000
Payments for Repurchase of Redeemable Noncontrolling Interest		2,800,000
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests		4,700,000
Henglong and Jiulong [Member] | Noncontrolling Interest [Member]
Additional Paid In Capital [Line Items]
Adjustments to Additional Paid in Capital, Other		$ 29,800,000

[1] On August 11, 2014, the Company entered into the Exchange Agreement with Jiulong Machinery Electricity, under which the Company issued 3,260,000 and 818,000 of its common shares in consideration for the acquisition of the 20% and 19% equity interests in Henglong and Jiulong, respectively, held by Jiulong Machinery Electricity. On September 26, 2014, the Company obtained the 20% and 19% equity interests in Henglong and Jiulong, respectively, and completed its share registrations with the local government administrative bureau. The Company owned 100% of the equity interests in both Henglong and Jiulong as of September 30, 2014. The Company’s acquisitions of the non-controlling interests were accounted for as equity transactions in the year ended December 31, 2014. The total carrying value for the non-controlling interests in both Henglong and Jiulong was $34.5 million, including the accumulated other comprehensive income of $4.7 million related to the noncontrolling interests acquired and other non-controlling interest of $29.8 million. Therefore, the total carrying value of $34.5 million for the non-controlling interests acquired was reclassified from non-controlling interests to the controlling interest’s equity as of September 30, 2014. On October 13, 2014, the Company completed its issuance of 4,078,000 common shares to nominee holders designated by Jiulong Machinery Electricity. The fair market value of the Company’s common stock issued was $37.3 million or $9.15 per share, which was determined on the issuance date of the common shares. The difference between the fair market value of $37.3 million for the Company’s common shares issued and the carrying value of $34.5 million for the non-controlling interest acquired of $2.8 million was recorded as a reduction of additional paid-in capital. Additional paid-in capital of the Company was also decreased by $4.7 million and the accumulated other comprehensive income attributable to Henglong and Jiulong was increased by a corresponding amount.