CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)	Common Stock	Additional Paid-in Capital	Accumulated (Deficit)	Accumulated Other Comprehensive Income (Loss)	Treasury Stock	Total
Accumulated other comprehensive income (loss) beginning balance period, net of tax at Dec. 31, 2017	$ 49,000	$ 1,084,889,000	$ (132,122,000)	$ (2,810,000)	$ (15,003,000)	$ 935,003,000
Beginning Balance (in shares) at Dec. 31, 2017	48,684,943
Increase (decrease) in shareholders' equity
Net income			73,638,000			73,638,000
Other comprehensive income (loss)				(9,609,000)		(9,609,000)
Issuance of treasury stock for employee stock purchase plan		(295,000)			724,000	429,000
Issuance of treasury stock for employee stock purchase plan (in shares)	14,828
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(6,059,000)			4,924,000	(1,135,000)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)	104,637
Tax Cuts and Jobs Act of 2017 reclassification			605,000	(605,000)
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax		(2,505,000)			2,891,000	386,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	55,901
Cash dividends common stock			(29,238,000)			(29,238,000)
Stock dividend equivalents restricted stock units		415,000	(415,000)
Stock-based compensation		2,666,000				2,666,000
Accumulated other comprehensive income (loss) ending balance period, net of tax at Sep. 30, 2018	$ 49,000	1,079,111,000	(87,532,000)	(13,024,000)	(6,464,000)	972,140,000
Ending Balance (in shares) at Sep. 30, 2018	48,860,309
Accumulated other comprehensive income (loss) beginning balance period, net of tax at Jun. 30, 2018	$ 49,000	1,082,323,000	(104,504,000)	(10,865,000)	(9,821,000)	957,182,000
Beginning Balance (in shares) at Jun. 30, 2018	48,776,404
Increase (decrease) in shareholders' equity
Net income			26,859,000			26,859,000
Other comprehensive income (loss)				(2,159,000)		(2,159,000)
Issuance of treasury stock for employee stock purchase plan		33,000			58,000	91,000
Issuance of treasury stock for employee stock purchase plan (in shares)	3,080
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(4,184,000)			3,121,000	(1,063,000)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)	72,805
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax		(138,000)			178,000	40,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	8,020
Cash dividends common stock			(9,756,000)			(9,756,000)
Stock dividend equivalents restricted stock units		133,000	(131,000)			2,000
Stock-based compensation		944,000				944,000
Accumulated other comprehensive income (loss) ending balance period, net of tax at Sep. 30, 2018	$ 49,000	1,079,111,000	(87,532,000)	(13,024,000)	(6,464,000)	972,140,000
Ending Balance (in shares) at Sep. 30, 2018	48,860,309
Accumulated other comprehensive income (loss) beginning balance period, net of tax at Dec. 31, 2018	$ 49,000	1,080,084,000	(72,167,000)	(6,812,000)	(6,190,000)	994,964,000
Beginning Balance (in shares) at Dec. 31, 2018	48,874,836
Increase (decrease) in shareholders' equity
Net income			74,382,000			74,382,000
Other comprehensive income (loss)				24,203,000		24,203,000
Repurchase of stock					(13,323,000)	(13,323,000)
Repurchase of stock (in shares)	(527,396)
Stock issued in acquisition of Banc Ed, net of stock issuance costs	$ 7,000	166,274,000				166,281,000
Stock issued in acquisition of Banc Ed, net of stock issuance costs (in shares)	6,725,152
Issuance of treasury stock for employee stock purchase plan		100,000			389,000	489,000
Issuance of treasury stock for employee stock purchase plan (in shares)	20,528
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(2,541,000)			345,000	(2,196,000)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)	91,032
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax		(97,000)			1,621,000	1,524,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	13,125
Cash dividends common stock			(33,579,000)			(33,579,000)
Stock dividend equivalents restricted stock units		504,000	(504,000)
Stock-based compensation		3,236,000				3,236,000
Accumulated other comprehensive income (loss) ending balance period, net of tax at Sep. 30, 2019	$ 56,000	1,247,560,000	(31,868,000)	17,391,000	(17,158,000)	1,215,981,000
Ending Balance (in shares) at Sep. 30, 2019	55,197,277
Accumulated other comprehensive income (loss) beginning balance period, net of tax at Jun. 30, 2019	$ 56,000	1,246,160,000	(44,878,000)	14,627,000	(12,357,000)	1,203,608,000
Beginning Balance (in shares) at Jun. 30, 2019	55,386,636
Increase (decrease) in shareholders' equity
Net income			24,828,000			24,828,000
Other comprehensive income (loss)				2,764,000		2,764,000
Repurchase of stock					(4,890,000)	(4,890,000)
Repurchase of stock (in shares)	(194,062)
Issuance of treasury stock for employee stock purchase plan		21,000			83,000	104,000
Issuance of treasury stock for employee stock purchase plan (in shares)	4,378
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(6,000)				(6,000)
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax		(6,000)			6,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	325
Cash dividends common stock			(11,632,000)			(11,632,000)
Stock dividend equivalents restricted stock units		186,000	(186,000)
Stock-based compensation		1,205,000				1,205,000
Accumulated other comprehensive income (loss) ending balance period, net of tax at Sep. 30, 2019	$ 56,000	$ 1,247,560,000	$ (31,868,000)	$ 17,391,000	$ (17,158,000)	$ 1,215,981,000
Ending Balance (in shares) at Sep. 30, 2019	55,197,277