CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Thousands	Total	Common Stock Issued	Common Stock Treasury	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balances at Dec. 31, 2016	$ 137,563	$ 140,625	$ (760,391)	$ 172,101	$ 1,150,688	$ (606,722)	$ 41,262
Increase (Decrease) in Stockholders' Equity
Net income	29,868				27,928		1,940
Cash dividends declared:	(1,769)						(1,769)
Total other comprehensive income (loss), net of deferred income taxes of $(3,442) and $1,671 in 2018 and 2017, respectively	16,521					14,987	1,534
Stock Appreciation Rights exercised, net 22,584 shares and 7,441 shares in 2018 and 2017, respectively	(49)	13	(49)	(13)
Vesting of restricted stock units and other stock grants, net 369,498 shares and 236,335 shares in 2018 and 2017, respectively	(1,277)	401	(1,277)	(401)
Amortization of unearned portion of stock-based compensation, net of forfeitures	5,642			5,642
Balances at Jun. 30, 2017	186,896	141,039	(761,717)	178,435	1,177,907	(591,735)	42,967
Increase (Decrease) in Stockholders' Equity
Adoption of new accounting standards (See Note 2)	397			1,106	(709)
Net income	19,731
Total other comprehensive income (loss), net of deferred income taxes of $(3,442) and $1,671 in 2018 and 2017, respectively	(864)
Balances at Jun. 30, 2017	186,896	141,039	(761,717)	178,435	1,177,907	(591,735)	42,967
Balances at Dec. 31, 2017	215,165	141,110	(762,079)	180,201	1,157,801	(546,582)	44,714
Increase (Decrease) in Stockholders' Equity
Net income	62,288				58,297		3,991
Cash dividends declared:	(5,521)						(5,521)
Sale of subsidiary shares to noncontrolling interest	477						477
Total other comprehensive income (loss), net of deferred income taxes of $(3,442) and $1,671 in 2018 and 2017, respectively	(11,027)					(9,787)	(1,240)
Stock Appreciation Rights exercised, net 22,584 shares and 7,441 shares in 2018 and 2017, respectively	(201)	39	(201)	(39)
Vesting of restricted stock units and other stock grants, net 369,498 shares and 236,335 shares in 2018 and 2017, respectively	(3,415)	663	(3,415)	(663)
Amortization of unearned portion of stock-based compensation, net of forfeitures	6,013			6,013
Balances at Jun. 30, 2018	266,153	141,812	(765,695)	185,512	1,219,992	(557,889)	42,421
Increase (Decrease) in Stockholders' Equity
Adoption of new accounting standards (See Note 2)	2,374				3,894	(1,520)
Net income	42,711
Total other comprehensive income (loss), net of deferred income taxes of $(3,442) and $1,671 in 2018 and 2017, respectively	(17,190)
Balances at Jun. 30, 2018	$ 266,153	$ 141,812	$ (765,695)	$ 185,512	1,219,992	$ (557,889)	$ 42,421
Increase (Decrease) in Stockholders' Equity
Adoption of new accounting standards (See Note 2)					$ 100