Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Common Stock, Shares, Outstanding	33,024,882		32,965,692
Stockholders' Equity Attributable to Parent	$ 1,715,371	$ 1,679,656	$ 1,702,685	$ 1,708,143
Held In Rabbi Trust At Cost [Member]
Stockholders' Equity Attributable to Parent	$ (3,080)	$ (4,604)	(3,066)	(4,735)
Retained Earnings
Cash dividends declared per common share (in dollars per share)	$ 0.48	$ 0.46
Stockholders' Equity Attributable to Parent	$ 741,883	$ 667,084	716,024	654,182
Deferred Compensation, Share-based Payments [Member]
Stockholders' Equity Attributable to Parent	3,080	4,604	3,066	4,735
AOCI Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent	27,157	49,728	40,695	18,169
Common Stock [Member]
Stockholders' Equity Attributable to Parent	329	331	328	342
Additional Paid-in Capital [Member]
Stockholders' Equity Attributable to Parent	$ 946,002	$ 962,513	$ 945,638	$ 1,035,450
Common Class A [Member]
Common Stock, Shares, Outstanding	33,024,882	33,260,005	32,965,692	34,377,388

Aggregate dividends declared during the period for each share of common stock outstanding.

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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