Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Common stock [Member]	Additional paid-in capital ("APIC") [Member]	Retained earnings [Member]	Accumulated other comprehensive income (loss) [Member]	Non-controlling interest ("NCI") [Member]	Contingently Redeemable Performance Share Units [Member]	Total
Balance at Dec. 31, 2018	$ 181,780	$ 56,885	$ 648,255	$ (56,277)	$ 5,067	$ 923	$ 835,710
Balance, shares at Dec. 31, 2018	108,682,030
Net income			72,200		103		72,303
Other comprehensive loss				828	(5)		823
Comprehensive income			72,200	828	98		73,126
Stock option exercises	$ 5,668	(1,544)					4,124
Stock option exercises, shares	181,359
Issuance of common stock related to vesting of share units	$ 5,149	(10,064)					(4,915)
Issuance of common stock related to vesting of share units, shares	196,959
Stock option compensation expense		3,199					3,199
Equity-classified PSU expense		5,810				93	5,810
Equity-classified PSU dividend equivalents		347	(380)			33	(33)
Cash dividends paid			(39,160)				(39,160)
Shares repurchased	$ (42,012)						(42,012)
Shares repurchased, shares	(1,223,674)
Balance at Jun. 30, 2019	$ 150,585	54,633	680,915	(55,449)	5,165	1,049	835,849
Balance, shares at Jun. 30, 2019	107,836,674
Balance at Mar. 31, 2019	$ 189,297	50,054	646,614	(57,899)	5,063	984	833,129
Balance, shares at Mar. 31, 2019	108,958,906
Net income			54,036		95		54,131
Other comprehensive loss				2,450	7		2,457
Comprehensive income			54,036	2,450	102		56,588
Stock option exercises	$ 3,190	(694)					2,496
Stock option exercises, shares	98,433
Issuance of common stock related to vesting of share units	$ 110						110
Issuance of common stock related to vesting of share units, shares	3,009
Stock option compensation expense		1,660					1,660
Equity-classified PSU expense		3,488				47	3,488
Equity-classified PSU dividend equivalents		125	(143)			18	(18)
Cash dividends paid			(19,592)				(19,592)
Shares repurchased	$ (42,012)						(42,012)
Shares repurchased, shares	(1,223,674)
Balance at Jun. 30, 2019	$ 150,585	54,633	680,915	(55,449)	5,165	$ 1,049	835,849
Balance, shares at Jun. 30, 2019	107,836,674
Balance at Dec. 31, 2019	$ 194,771	52,110	714,051	(59,099)	5,154		906,987
Balance, shares at Dec. 31, 2019	109,337,781
Net income			75,851		97		75,948
Other comprehensive loss				(5,108)	3		(5,105)
Comprehensive income			75,851	(5,108)	100		70,843
Stock option exercises	$ 24,141	(4,716)					$ 19,425
Stock option exercises, shares	679,277						679,277
Issuance of common stock related to vesting of share units	$ 3,513	(7,451)					$ (3,938)
Issuance of common stock related to vesting of share units, shares	138,791
Stock option compensation expense		2,730					2,730
Equity-classified PSU expense		5,017					5,017
Equity-classified PSU dividend equivalents		268	(268)
Cash dividends paid			(43,586)				(43,586)
Shares repurchased	$ (53,170)						(53,170)
Shares repurchased, shares	(1,525,312)
Balance at Jun. 30, 2020	$ 169,255	47,958	746,048	(64,207)	5,254		904,308
Balance, shares at Jun. 30, 2020	108,630,537
Balance at Mar. 31, 2020	$ 153,801	46,147	714,816	(74,959)	5,166		844,971
Balance, shares at Mar. 31, 2020	108,198,739
Net income			53,043		76		53,119
Other comprehensive loss				10,752	12		10,764
Comprehensive income			53,043	10,752	88		63,883
Stock option exercises	$ 15,457	(3,086)					12,371
Stock option exercises, shares	431,831
Issuance of common stock related to vesting of share units	$ (3)	(7)					(10)
Issuance of common stock related to vesting of share units, shares	(33)
Stock option compensation expense		1,543					1,543
Equity-classified PSU expense		3,231					3,231
Equity-classified PSU dividend equivalents		130	(130)
Cash dividends paid			(21,681)				(21,681)
Balance at Jun. 30, 2020	$ 169,255	$ 47,958	$ 746,048	$ (64,207)	$ 5,254		$ 904,308
Balance, shares at Jun. 30, 2020	108,630,537