Consolidated Statements of Stockholders' Equity (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Stockholders' Equity Attributable to Parent	$ 1,682,324	$ 998,305	$ 1,682,324	$ 998,305	$ 1,636,003	$ 1,073,490	$ 977,065	$ 943,809
Held In Rabbi Trust At Cost [Member]
Stockholders' Equity Attributable to Parent	$ (4,713)	$ (4,784)	$ (4,713)	$ (4,784)	(4,648)	(4,718)	(4,653)	(4,590)
Retained Earnings
Cash dividends declared per common share (in dollars per share)	$ 0.44	$ 0.38	$ 1.32	$ 1.14
Stockholders' Equity Attributable to Parent	$ 621,831	$ 527,473	$ 621,831	$ 527,473	585,111	546,736	504,926	465,937
Deferred Compensation, Share-based Payments [Member]
Stockholders' Equity Attributable to Parent	4,713	4,784	4,713	4,784	4,648	4,718	4,653	4,590
AOCI Attributable to Parent [Member]
Stockholders' Equity Attributable to Parent	26,202	(12,664)	26,202	(12,664)	20,956	(1,173)	(10,114)	(1,831)
Common Stock [Member]
Stockholders' Equity Attributable to Parent	342	274	342	274	342	279	274	273
Additional Paid-in Capital [Member]
Stockholders' Equity Attributable to Parent	$ 1,033,949	$ 483,222	$ 1,033,949	$ 483,222	$ 1,029,594	$ 527,648	$ 481,979	$ 479,430
Common Class A [Member]
Common Stock, Shares, Outstanding	34,366,781	27,540,843	34,366,781	27,540,843	34,321,061	28,080,408	27,532,524	27,450,190

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

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