Unaudited Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance at Dec. 31, 2018	$ 1,439,768	$ 718	$ 1,097,758	$ 1,029,518	$ (71,397)	$ (616,829)
Increase (Decrease) in Stockholders' Equity
Net loss	(56,256)			(56,256)
Currency translation adjustments (excluding intercompany advances)	(4,841)				(4,841)
Currency translation adjustments on intercompany advances	(694)				(694)
Stock-based compensation expense:
Restricted stock	12,769	8	12,761
Stock options	53		53
Stock repurchases	(757)					(757)
Surrender of stock to settle taxes on restricted stock awards	(3,698)					(3,698)
Ending balance at Sep. 30, 2019	1,386,344	726	1,110,572	973,262	(76,932)	(621,284)
Beginning balance at Jun. 30, 2019	1,419,728	726	1,106,340	1,005,130	(71,260)	(621,208)
Increase (Decrease) in Stockholders' Equity
Net loss	(31,868)			(31,868)
Currency translation adjustments (excluding intercompany advances)	(4,448)				(4,448)
Currency translation adjustments on intercompany advances	(1,224)				(1,224)
Stock-based compensation expense:
Restricted stock	4,232	0	4,232
Stock options	0
Stock repurchases	0
Surrender of stock to settle taxes on restricted stock awards	(76)					(76)
Ending balance at Sep. 30, 2019	1,386,344	726	1,110,572	973,262	(76,932)	(621,284)
Beginning balance at Dec. 31, 2019	1,223,967	726	1,114,521	797,710	(67,746)	(621,244)
Increase (Decrease) in Stockholders' Equity
Net loss	(449,636)			(449,636)
Currency translation adjustments (excluding intercompany advances)	(4,524)				(4,524)
Currency translation adjustments on intercompany advances	(8,140)				(8,140)
Stock-based compensation expense:
Restricted stock	5,346	7	5,339
Surrender of stock to settle taxes on restricted stock awards	(2,675)					(2,675)
Ending balance at Sep. 30, 2020	764,338	733	1,119,860	348,074	(80,410)	(623,919)
Beginning balance at Jun. 30, 2020	778,869	733	1,117,771	368,043	(83,767)	(623,911)
Increase (Decrease) in Stockholders' Equity
Net loss	(19,969)			(19,969)
Currency translation adjustments (excluding intercompany advances)	4,624				4,624
Currency translation adjustments on intercompany advances	(1,267)				(1,267)
Stock-based compensation expense:
Restricted stock	2,089	0	2,089
Surrender of stock to settle taxes on restricted stock awards	(8)					(8)
Ending balance at Sep. 30, 2020	$ 764,338	$ 733	$ 1,119,860	$ 348,074	$ (80,410)	$ (623,919)