CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Ordinary share capital	Additional paid-in capital	Retained earnings	Shareholders' equity attributable to shareholders	Non-controlling interest in joint venture
Balance at Dec. 31, 2015	$ 848,773	$ 3,703	$ 496,401	$ 325,287	$ 825,391	$ 23,382
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issue of Class A ordinary shares, net of forfeitures	33	33	0	0	33	0
Share-based compensation expense, net of forfeitures	3,096	0	3,096	0	3,096	0
Non-controlling interest contribution into (withdrawal from) joint venture, net	(10,000)	0	0	0	0	(10,000)
Income (loss) attributable to non-controlling interest in joint venture	963	0	0	0	0	963
Net income (loss)	(4,315)	0	0	(4,315)	(4,315)	0
Balance at Sep. 30, 2016	838,550	3,736	499,497	320,972	824,205	14,345
Balance at Dec. 31, 2016	891,687	3,737	500,337	370,168	874,242	17,445
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issue of Class A ordinary shares, net of forfeitures	12	12	0	0	12	0
Repurchase of Class A ordinary shares	(2,819)	(14)	(1,861)	(944)	(2,819)	0
Share-based compensation expense, net of forfeitures	3,290	0	3,290	0	3,290	0
Income (loss) attributable to non-controlling interest in joint venture	780	0	0	0	0	780
Net income (loss)	(7,220)	0	0	(7,220)	(7,220)	0
Balance at Sep. 30, 2017	$ 885,730	$ 3,735	$ 501,766	$ 362,004	$ 867,505	$ 18,225