Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	AOCI Attributable to Parent [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance (in shares) at Dec. 31, 2013	79,589,869
Beginning balance, loss, net of tax at Dec. 31, 2013	$ 838	$ 784,489	$ (29,729)	$ 829,109	$ (125,736)	$ 1,458,971
Dividend Reinvestment Plan (in shares)	116,957					116,957
Dividend Reinvestment Plan	$ 1	2,847				$ 2,848
Restricted stock units vested (in shares)	88,537
Restricted stock units vested	$ 1					1
Shares withheld related to net share settlement of RSUs		(850)				(850)
Stock issued to directors (in shares)	13,690
Stock issued to directors		350				$ 350
Stock options exercised (in shares)	5,500					5,500
Stock options exercised		128				$ 128
Tax short-fall from stock options		(1,285)				(1,285)
Stock -based compensation		3,840				3,840
Cash dividends				(23,105)		(23,105)
Change in other comprehensive loss			24,160			24,160
Net income				137,830		137,830
Balance (in shares) at Dec. 31, 2014	79,814,553
Ending balance, loss, net of tax at Dec. 31, 2014	$ 840	789,519	(5,569)	943,834	(125,736)	$ 1,602,888
Dividend Reinvestment Plan (in shares)	148,582					148,582
Dividend Reinvestment Plan	$ 2	4,173				$ 4,175
Restricted stock units vested (in shares)	18,955
Restricted stock units vested
Shares withheld related to net share settlement of RSUs		(227)				(227)
Stock issued to directors (in shares)	17,974
Stock issued to directors		495				$ 495
Stock options exercised (in shares)	214,580					214,580
Stock options exercised	$ 2	5,012				$ 5,014
Tax short-fall from stock options		(5,348)				(5,348)
Stock -based compensation		4,455				4,455
Cash dividends				(45,283)		(45,283)
Change in other comprehensive loss			(2,857)			(2,857)
Net income				161,109		161,109
Balance (in shares) at Dec. 31, 2015	80,806,116
Ending balance, loss, net of tax at Dec. 31, 2015	$ 870	880,822	(8,426)	1,059,660	(185,148)	1,747,778
Warrant exercised (in shares)	369
Equity consideration for acquisition (in shares)	2,580,353
Equity consideration for acquisition	$ 26	82,743				82,769
Purchases of treasury stock (in shares)	(1,989,250)
Purchases of treasury stock					(59,412)	$ (59,412)
Dividend Reinvestment Plan (in shares)	72,231					72,231
Dividend Reinvestment Plan	$ 1	2,276				$ 2,277
Restricted stock units vested (in shares)	10,325
Restricted stock units vested
Shares withheld related to net share settlement of RSUs		(103)				(103)
Stock issued to directors (in shares)	19,602
Stock issued to directors		550				$ 550
Stock options exercised (in shares)	327,830					327,830
Stock options exercised	$ 3	7,658				$ 7,661
Tax short-fall from stock options		(132)				(132)
Stock -based compensation		4,413				4,413
Cash dividends				(59,274)		(59,274)
Change in other comprehensive loss			4,711			4,711
Net income				175,099		175,099
Balance (in shares) at Dec. 31, 2016	79,610,277
Ending balance, loss, net of tax at Dec. 31, 2016	$ 878	895,480	(3,715)	1,175,485	(239,589)	1,828,539
Warrant exercised (in shares)	388,001
Purchases of treasury stock (in shares)	(2,013,828)
Purchases of treasury stock					$ (54,441)	$ (54,441)