Consolidated Statements of Equity (Unaudited) - USD ($)	Common Stock [Member] Restricted Stock Units (RSUs) [Member]	Common Stock [Member] Performance Shares [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Noncontrolling Interest [Member]	Restricted Stock Units (RSUs) [Member]	Performance Shares [Member]	Total
Balance (in shares) at Dec. 31, 2017			32,462,542
Issuance of common stock upon stock option exercises (in shares)			0
Issuance of shares pursuant to restricted stock units (in shares)	295,420	296,909
Issuance of shares pursuant to deferred stock units (in shares)			20,939
Shares repurchased and retired (in shares)			(772,172)
Balance (in shares) at Jun. 30, 2018			32,303,638
Balance at Dec. 31, 2017			$ 325,000	$ 140,749,000	$ 386,008,000	$ (32,836,000)	$ 10,810,000			$ 505,056,000
Issuance of common stock upon stock option exercises			0	0						0
Issuance of shares pursuant to restricted stock units	$ 3,000	$ 3,000						$ 3,000	$ 3,000
Issuance of shares pursuant to deferred stock units			0							0
Shares repurchased and retired			(8,000)	(18,601,000)						(18,609,000)
Balance at Jun. 30, 2018			$ 323,000	127,242,000	392,128,000	(35,688,000)	10,433,000			494,438,000
Equity-based compensation expense				5,094,000						5,094,000
Cumulative effect adjustment (see Revenues: Note 3)					268,000					268,000
Net income (loss)					5,852,000		(130,000)			5,722,000
Currency translation adjustment and derivative transactions, net						(2,852,000)	(247,000)			(3,099,000)
Distributions to non-controlling interests							0			0
Balance (in shares) at Mar. 31, 2018			32,467,823
Issuance of common stock upon stock option exercises (in shares)			0
Issuance of shares pursuant to restricted stock units (in shares)	20,036	0
Issuance of shares pursuant to deferred stock units (in shares)			16,371
Shares repurchased and retired (in shares)			(200,592)
Balance (in shares) at Jun. 30, 2018			32,303,638
Balance at Mar. 31, 2018			$ 325,000	129,237,000	384,207,000	(30,174,000)	11,456,000			495,051,000
Issuance of common stock upon stock option exercises			0	0						0
Issuance of shares pursuant to restricted stock units	$ 0	$ 0						0	0
Issuance of shares pursuant to deferred stock units			0							0
Shares repurchased and retired			(2,000)	(4,931,000)						(4,933,000)
Balance at Jun. 30, 2018			$ 323,000	127,242,000	392,128,000	(35,688,000)	10,433,000			494,438,000
Equity-based compensation expense				2,936,000						2,936,000
Cumulative effect adjustment (see Revenues: Note 3)					0					0
Net income (loss)					7,921,000		(723,000)			7,198,000
Currency translation adjustment and derivative transactions, net						(5,514,000)	(300,000)			(5,814,000)
Distributions to non-controlling interests							0			$ 0
Balance (in shares) at Dec. 31, 2018			31,922,409							31,922,409
Issuance of common stock upon stock option exercises (in shares)			52,783
Issuance of shares pursuant to restricted stock units (in shares)	205,274	111,158
Issuance of shares pursuant to deferred stock units (in shares)			77,486
Shares repurchased and retired (in shares)			(1,427,716)
Balance (in shares) at Jun. 30, 2019			30,941,394							30,941,394
Balance at Dec. 31, 2018			$ 319,000	122,818,000	379,890,000	(40,290,000)	7,450,000			$ 470,187,000
Issuance of common stock upon stock option exercises			1,000	955,000						956,000
Issuance of shares pursuant to restricted stock units	$ 2,000	$ 1,000						2,000	1,000
Issuance of shares pursuant to deferred stock units			1,000							1,000
Shares repurchased and retired			(15,000)	(25,156,000)						(25,171,000)
Balance at Jun. 30, 2019			$ 309,000	102,841,000	367,523,000	(42,940,000)	6,290,000			434,023,000
Equity-based compensation expense				4,224,000						4,224,000
Cumulative effect adjustment (see Revenues: Note 3)					0					0
Net income (loss)					(12,367,000)		229,000			(12,138,000)
Currency translation adjustment and derivative transactions, net						(2,650,000)	20,000			(2,630,000)
Distributions to non-controlling interests							(1,409,000)			$ (1,409,000)
Balance (in shares) at Mar. 31, 2019			31,491,872
Issuance of common stock upon stock option exercises (in shares)			0							52,783
Issuance of shares pursuant to restricted stock units (in shares)	33,699	502
Issuance of shares pursuant to deferred stock units (in shares)			68,048
Shares repurchased and retired (in shares)			(652,727)
Balance (in shares) at Jun. 30, 2019			30,941,394							30,941,394
Balance at Mar. 31, 2019			$ 315,000	111,597,000	375,889,000	(40,508,000)	7,277,000			$ 454,570,000
Issuance of common stock upon stock option exercises			0	0						0
Issuance of shares pursuant to restricted stock units	$ 0	$ 0						$ 0	$ 0
Issuance of shares pursuant to deferred stock units			1,000							1,000
Shares repurchased and retired			(7,000)	(10,973,000)						(10,980,000)
Balance at Jun. 30, 2019			$ 309,000	102,841,000	367,523,000	(42,940,000)	6,290,000			434,023,000
Equity-based compensation expense				$ 2,217,000						2,217,000
Cumulative effect adjustment (see Revenues: Note 3)					0					0
Net income (loss)					$ (8,366,000)		219,000			(8,147,000)
Currency translation adjustment and derivative transactions, net						$ (2,432,000)	107,000			(2,325,000)
Distributions to non-controlling interests							$ (1,313,000)			$ (1,313,000)