Consolidated Statements of Changes in Shareholders' Equity - USD ($) $ in Thousands	Total	Preferred Stock [Member]	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Balance, value at Dec. 31, 2015	$ 1,242,128	$ 2,217	$ 990,281	$ 255,925	$ (6,295)
Balance (in shares) at Dec. 31, 2015		9,000	57,724,000
Net income	104,866			104,866
Other comprehensive income	(12,704)				(12,704)
Stock Adjustment Value Deferred Compensation	(11)
Issuance of common stock - stock option and other plans, shares			50,000
Issuance of common stock - stock option and other plans, value	1,349		$ 1,349
Issuance of common stock - restricted stock awards, net of canceled awards, shares			306,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	5,009		$ 5,009
Tax benefit deficiency associated with share-based compensation	334		$ 334
Purchase and retirement of common stock (in shares)			(38,000)
Purchase and retirement of common stock, value	(1,125)		$ (1,125)
Dividends, Preferred Stock, Cash	(157)			(157)
Cash dividends paid on common stock	(88,677)			(88,677)
Balance, value at Dec. 31, 2016	$ 1,251,012	$ 2,217	$ 995,837	271,957	(18,999)
Balance (in shares) at Dec. 31, 2016		9,000	58,042,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 1.53
Common Stock, Dividends, Per Share, Cash Paid	$ 1.53
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-09 [Member]	$ 67		$ 184	(117)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]	0			4,082	(4,082)
Net income	112,828			112,828
Other comprehensive income	856				856
Issuance of common stock, net of offering costs, shares			14,642,000
Issuance of common stock, net of offering costs, value	636,385		$ 636,385
Stock Adjustment Value Deferred Compensation	1		$ 1
Issuance of common stock - stock option and other plans, shares			49,000
Issuance of common stock - stock option and other plans, value	1,980		$ 1,980
Issuance of common stock - restricted stock awards, net of canceled awards, shares			241,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	7,745		$ 7,745
Conversion of Stock, Shares Converted		(9,000)
Conversion of Stock, Amount Converted		$ (2,217)
Conversion of Stock, Shares Issued			102,000
Conversion of Stock, Amount Issued	0		$ 2,217
Purchase and retirement of common stock (in shares)			(56,000)
Purchase and retirement of common stock, value	(2,299)		$ (2,299)
Stock Redeemed or Called During Period, Value	(7,345)		(7,345)
Cash dividends paid on common stock	(51,308)			(51,308)
Balance, value at Dec. 31, 2017	$ 1,949,922	$ 0	$ 1,634,705	337,442	(22,225)
Balance (in shares) at Dec. 31, 2017		0	73,020,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 0.00
Common Stock, Dividends, Per Share, Cash Paid	$ 0.88
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]					(4,082)
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2016-01 [Member]	$ 0			(157)	157
Net income	172,882			172,882
Other comprehensive income	(13,237)				(13,237)
Stock Adjustment Value Deferred Compensation	$ 7		$ 7
Issuance of common stock - stock option and other plans, shares	1,112		46,000
Issuance of common stock - stock option and other plans, value	$ 1,857		$ 1,857
Issuance of common stock - restricted stock awards, net of canceled awards, shares			246,000
Issuance of common stock - restricted stock awards, net of canceled awards, value	8,354		$ 8,354
Purchase and retirement of common stock (in shares)			(63,000)
Purchase and retirement of common stock, value	(2,677)		$ (2,677)
Cash dividends paid on common stock	(83,459)			(83,459)
Balance, value at Dec. 31, 2018	$ 2,033,649	$ 0	$ 1,642,246	$ 426,708	$ (35,305)
Balance (in shares) at Dec. 31, 2018		0	73,249,000
Preferred Stock, Dividends, Per Share, Cash Paid	$ 0.00
Common Stock, Dividends, Per Share, Cash Paid	$ 1.14