CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Non-Controlling Interests	Total
BALANCE at Dec. 31, 2015	$ 411	$ (46,845)	$ 323,765	$ 69,390	$ 18,284	$ 365,005
BALANCE (in shares) at Dec. 31, 2015	41,123,365
BALANCE (in shares) at Dec. 31, 2015		(3,696,781)
Increase (Decrease) in Stockholders' Equity
Net income				64,896		64,896
Issuance of Stock:
Issuance of shares for options exercised		$ 1,568	10			1,578
Issuance of shares for options exercised (in shares)		111,761
Issuance of restricted stock & performance stock		$ 2,282	(306)			1,976
Issuance of restricted stock & performance stock (in shares)		172,727
Shares received in lieu of tax withholding payment on vested restricted stock		$ (1,304)				(1,304)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(41,788)
Stock-based compensation			3,502			3,502
Dividends				(10,264)		(10,264)
Acquisition of noncontrolling interests			(17,346)		$ (18,284)	(35,630)
Share repurchase		$ (13,088)				(13,088)
Share repurchase (in shares)		(460,170)
BALANCE at Dec. 31, 2016	$ 411	$ (57,387)	309,625	123,984		376,633
BALANCE (in shares) at Dec. 31, 2016	41,123,365
BALANCE (in shares) at Dec. 31, 2016		(3,914,251)
Cumulative effect of change in accounting principle at Dec. 31, 2016				(38)		(38)
Increase (Decrease) in Stockholders' Equity
Net income				55,272		55,272
Issuance of Stock:
Issuance of shares for options exercised		$ 2,257	(205)			2,052
Issuance of shares for options exercised (in shares)		(145,746)
Issuance of restricted stock & performance stock		$ 2,037	(421)			1,616
Issuance of restricted stock & performance stock (in shares)		(134,646)
Shares received in lieu of tax withholding payment on vested restricted stock		$ (1,419)				(1,419)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(39,335)
Stock-based compensation			3,785			3,785
Dividends				(10,987)		(10,987)
Share repurchase		$ (9,007)				(9,007)
Share repurchase (in shares)		(263,097)
BALANCE at Dec. 31, 2017	$ 411	$ (63,519)	312,784	168,269		$ 417,945
BALANCE (in shares) at Dec. 31, 2017	41,123,365					41,123,365
BALANCE (in shares) at Dec. 31, 2017		(3,936,291)				3,936,291
Increase (Decrease) in Stockholders' Equity
Net income				112,903		$ 112,903
Issuance of Stock:
Issuance of shares for options exercised		$ 3,618	(513)			3,105
Issuance of shares for options exercised (in shares)		(206,875)
Issuance of restricted stock & performance stock		$ 2,227	(4)			2,223
Issuance of restricted stock & performance stock (in shares)		(129,569)
Shares received in lieu of tax withholding payment on vested restricted stock		$ (1,540)				(1,540)
Shares received in lieu of tax withholding payment on vested restricted stock (in shares)		(36,967)
Stock-based compensation			4,212			4,212
Dividends				(12,268)		(12,268)
Share repurchase		$ (28,533)				(28,533)
Share repurchase (in shares)		(592,839)
BALANCE at Dec. 31, 2018	$ 411	$ (87,747)	$ 316,479	$ 268,904		$ 498,047
BALANCE (in shares) at Dec. 31, 2018	41,123,365					41,123,365
BALANCE (in shares) at Dec. 31, 2018		(4,229,653)				4,229,653