Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
BALANCE at Dec. 31, 2017	$ 1,184,782	$ 805	$ 102,563	$ 1,267,871	$ (15,835)	$ (170,622)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	167,910	0	0	168,148	(238)	0
Purchases of common stock	(72,165)	0	0	0	0	(72,165)
Dividends on common stock	(24,284)	0	0	(24,284)	0	0
Equity compensation activity, including excess tax benefits	(895)	0	(2,502)	0	0	1,607
Non-cash equity compensation expense	7,394	0	7,394	0	0	0
Cumulative effect of accounting change	2,011	0	0	2,011	0	0
BALANCE at Dec. 31, 2018	1,264,753	805	107,455	1,413,746	(16,073)	(241,180)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	168,289	0	0	166,944	1,345	0
Purchases of common stock	(42,301)	0	0	0	0	(42,301)
Dividends on common stock	(286,082)	0	0	(286,082)	0	0
Equity compensation activity, including excess tax benefits	(1,728)	0	(2,883)	0	0	1,155
Non-cash equity compensation expense	8,077	0	8,077	0	0	0
BALANCE at Dec. 31, 2019	1,111,008	805	112,649	1,294,608	(14,728)	(282,326)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income	160,973	0	0	169,078	(8,105)	0
Purchases of common stock	(56,521)	0	0	0	0	(56,521)
Dividends on common stock	(24,770)	0	0	(24,770)	0	0
Equity compensation activity, including excess tax benefits	(4,553)	0	(5,513)	0	0	960
Non-cash equity compensation expense	8,903	0	8,903	0	0	0
BALANCE at Dec. 31, 2020	$ 1,195,040	$ 805	$ 116,039	$ 1,438,916	$ (22,833)	$ (337,887)