CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Common Stock [Member] Restricted Stock [Member]	Common Stock [Member] Restricted Stock Units (RSUs) [Member]	Common Stock [Member]	Retained Earnings / (Accumulated deficit) [Member]	Accumulated Other Comprehensive Loss [Member]	Restricted Stock [Member]	Restricted Stock Units (RSUs) [Member]	Total
Balance, beginning at Dec. 31, 2017			$ 1,306,606	$ (180,545)	$ (40,407)			$ 1,085,654
Net loss				(95,898)				(95,898)
Other comprehensive income (loss)					16,588			16,588
Forfeitures of vested restricted stock awards			(499)					(499)
Compensation relating to stock option awards	$ 627	$ 924				$ 627	$ 924
Compensation relating to restricted stock units or restricted stock awards			652					652
Balance, ending at Sep. 30, 2018			1,308,310	(276,443)	(23,819)			1,008,048
Balance, beginning at Jun. 30, 2018			1,307,645	(228,657)	(28,447)			1,050,541
Net loss				(47,786)				(47,786)
Other comprehensive income (loss)					4,628			4,628
Forfeitures of vested restricted stock awards			(13)					(13)
Compensation relating to stock option awards	211	229				211	229
Compensation relating to restricted stock units or restricted stock awards			238					238
Balance, ending at Sep. 30, 2018			1,308,310	(276,443)	(23,819)			1,008,048
Balance, beginning at Dec. 31, 2018			1,309,269	(269,485)	(29,929)			1,009,855
Net loss				(16,721)				(16,721)
Other comprehensive income (loss)					(13,555)			(13,555)
Forfeitures of vested restricted stock awards			(369)					(369)
Compensation relating to stock option awards	667	1,462				667	1,462
Compensation relating to restricted stock units or restricted stock awards			783					783
Balance, ending at Sep. 30, 2019			1,311,812	(286,206)	(43,484)			982,122
Balance, beginning at Jun. 30, 2019			1,310,731	(275,111)	(40,282)			995,338
Net loss				(11,095)				(11,095)
Other comprehensive income (loss)					(3,202)			(3,202)
Forfeitures of vested restricted stock awards			(10)					(10)
Compensation relating to stock option awards	$ 233	$ 579				$ 233	$ 579
Compensation relating to restricted stock units or restricted stock awards			279					279
Balance, ending at Sep. 30, 2019			$ 1,311,812	$ (286,206)	$ (43,484)			$ 982,122