Consolidated Statements of Changes In Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance (in shares) at Dec. 31, 2017		102,717,000
Beginning balance at Dec. 31, 2017	$ 1,864,874	$ 1,123	$ 1,031,870	$ 1,074,990	$ (33,036)	$ (210,073)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	63,110			63,110
Other comprehensive income (loss)	(24,675)				(24,675)
Common dividends declared ($0.11 and $0.14 per common share for the quarter ended June 30, 2018 and 2019, respectively and $0.22 and $0.26 per common share for the six months ended June 30, 2018 and 2019, respectively)	(22,682)			(22,682)
Acquisitions, net of issuance costs	0
Common stock issued (in shares)		5,000
Common stock issued	829	$ 1	161			667
Restricted stock activity (in shares)		339,000
Restricted stock activity	(4,047)		(12,558)			8,511
Treasury stock issued to benefit plans (in shares)		(2,000)
Treasury stock issued to benefit plans	(42)		34			(76)
Share-based compensation expense	6,196		6,196
Ending balance (in shares) at Jun. 30, 2018		103,059,000
Ending balance at Jun. 30, 2018	1,883,563	$ 1,124	1,025,703	1,122,107	(64,400)	(200,971)
Beginning balance (in shares) at Mar. 31, 2018		103,092,000
Beginning balance at Mar. 31, 2018	1,869,287	$ 1,123	1,021,923	1,103,840	(57,531)	(200,068)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	29,600			29,600
Other comprehensive income (loss)	(6,869)				(6,869)
Common dividends declared ($0.11 and $0.14 per common share for the quarter ended June 30, 2018 and 2019, respectively and $0.22 and $0.26 per common share for the six months ended June 30, 2018 and 2019, respectively)	(11,333)			(11,333)
Common stock issued (in shares)		4,000
Common stock issued	68	$ 1	67
Restricted stock activity (in shares)		(38,000)
Restricted stock activity	(49)		872			(921)
Treasury stock issued to benefit plans (in shares)		1,000
Treasury stock issued to benefit plans	30		12			18
Share-based compensation expense	2,829		2,829
Ending balance (in shares) at Jun. 30, 2018		103,059,000
Ending balance at Jun. 30, 2018	$ 1,883,563	$ 1,124	1,025,703	1,122,107	(64,400)	(200,971)
Beginning balance (in shares) at Dec. 31, 2018	106,375,000	106,375,000
Beginning balance at Dec. 31, 2018	$ 2,054,998	$ 1,157	1,114,580	1,192,767	(52,512)	(200,994)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	93,072			93,072
Other comprehensive income (loss)	49,702				49,702
Common dividends declared ($0.11 and $0.14 per common share for the quarter ended June 30, 2018 and 2019, respectively and $0.22 and $0.26 per common share for the six months ended June 30, 2018 and 2019, respectively)	(28,340)			(28,340)
Repurchases of common stock (in shares)		(1,042,000)
Repurchases of common stock	(21,190)					(21,190)
Acquisitions, net of issuance costs (in shares)		4,879,000
Acquisitions, net of issuance costs	101,496	$ 47	97,351			4,098
Common stock issued (in shares)		30,000
Common stock issued	605	$ 0	(69)			674
Restricted stock activity (in shares)		353,000
Restricted stock activity	(3,770)		(13,320)			9,550
Treasury stock issued to benefit plans (in shares)		(6,000)
Treasury stock issued to benefit plans	(120)		(9)			(111)
Share-based compensation expense	$ 6,863		6,863
Ending balance (in shares) at Jun. 30, 2019	110,589,000	110,589,000
Ending balance at Jun. 30, 2019	$ 2,300,573	$ 1,204	1,205,396	1,304,756	(2,810)	(207,973)
Beginning balance (in shares) at Mar. 31, 2019		106,900,000
Beginning balance at Mar. 31, 2019	2,159,471	$ 1,157	1,103,991	1,273,245	(32,159)	(186,763)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	47,014			47,014
Other comprehensive income (loss)	29,349				29,349
Common dividends declared ($0.11 and $0.14 per common share for the quarter ended June 30, 2018 and 2019, respectively and $0.22 and $0.26 per common share for the six months ended June 30, 2018 and 2019, respectively)	(15,503)			(15,503)
Repurchases of common stock (in shares)		(1,042,000)
Repurchases of common stock	(21,190)					(21,190)
Acquisitions, net of issuance costs (in shares)		4,729,000
Acquisitions, net of issuance costs	98,212	$ 47	98,165
Common stock issued (in shares)		3,000
Common stock issued	68		68
Restricted stock activity (in shares)		1,000
Restricted stock activity	5		(7)			12
Treasury stock issued to benefit plans (in shares)		(2,000)
Treasury stock issued to benefit plans	(37)		(5)			(32)
Share-based compensation expense	$ 3,184		3,184
Ending balance (in shares) at Jun. 30, 2019	110,589,000	110,589,000
Ending balance at Jun. 30, 2019	$ 2,300,573	$ 1,204	$ 1,205,396	$ 1,304,756	$ (2,810)	$ (207,973)