CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($)	Common Stock	Additional Paid-in Capital	Accumulated (Deficit)	Accumulated Other Comprehensive Income (loss)	Treasury Stock	Total
Beginning Balance 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			46,779,000			46,779,000
Other comprehensive income (loss)				(7,450,000)		(7,450,000)
Issuance of treasury stock for employee stock purchase plan		(328,000)			666,000	338,000
Issuance of treasury stock for employee stock purchase plan (in shares)	11,748
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(1,875,000)			1,803,000	(72,000)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)	31,832
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		(2,367,000)			2,713,000	346,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	47,881
Cash dividends common stock			(19,482,000)			(19,482,000)
Stock dividend equivalents restricted stock units		282,000	(284,000)			(2,000)
Stock-based compensation		1,722,000				1,722,000
Ending Balance at Jun. 30, 2018	$ 49,000	1,082,323,000	(104,504,000)	(10,865,000)	(9,821,000)	957,182,000
Ending Balance (in shares) at Jun. 30, 2018	48,776,404
Beginning Balance at Mar. 31, 2018	$ 49,000	1,084,411,000	(119,467,000)	(9,674,000)	(13,173,000)	942,146,000
Beginning Balance (in shares) at Mar. 31, 2018	48,717,239
Increase (decrease) in shareholders' equity
Net income			24,862,000			24,862,000
Other comprehensive income (loss)				(1,191,000)		(1,191,000)
Issuance of treasury stock for employee stock purchase plan		(80,000)			172,000	92,000
Issuance of treasury stock for employee stock purchase plan (in shares)	3,030
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(1,875,000)			1,803,000	(72,000)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)	31,832
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax		(1,161,000)			1,377,000	216,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	24,303
Cash dividends common stock			(9,743,000)			(9,743,000)
Stock dividend equivalents restricted stock units		154,000	(156,000)			(2,000)
Stock-based compensation		874,000				874,000
Ending Balance at Jun. 30, 2018	$ 49,000	1,082,323,000	(104,504,000)	(10,865,000)	(9,821,000)	957,182,000
Ending Balance (in shares) at Jun. 30, 2018	48,776,404
Beginning Balance 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			49,554,000			49,554,000
Other comprehensive income (loss)				21,439,000		21,439,000
Repurchase of stock					(8,433,000)	(8,433,000)
Repurchase of stock (in shares)	(333,334)
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		79,000			306,000	385,000
Issuance of treasury stock for employee stock purchase plan (in shares)	16,150
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(2,535,000)			345,000	(2,190,000)
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		(91,000)			1,615,000	1,524,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	12,800
Cash dividends common stock			(21,947,000)			(21,947,000)
Stock dividend equivalents restricted stock units		318,000	(318,000)
Stock-based compensation		2,031,000				2,031,000
Ending Balance at Jun. 30, 2019	$ 56,000	1,246,160,000	(44,878,000)	14,627,000	(12,357,000)	1,203,608,000
Ending Balance (in shares) at Jun. 30, 2019	55,386,636
Beginning Balance at Mar. 31, 2019	$ 56,000	1,247,340,000	(57,125,000)	1,595,000	(5,725,000)	1,186,141,000
Beginning Balance (in shares) at Mar. 31, 2019	55,624,627
Increase (decrease) in shareholders' equity
Net income			24,085,000			24,085,000
Other comprehensive income (loss)				13,032,000		13,032,000
Repurchase of stock					(8,433,000)	(8,433,000)
Repurchase of stock (in shares)	(333,334)
Issuance of treasury stock for employee stock purchase plan		29,000			84,000	113,000
Issuance of treasury stock for employee stock purchase plan (in shares)	4,419
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax		(2,364,000)			174,000	(2,190,000)
Net issuance of treasury stock for restricted/deferred stock unit vesting and related tax (in shares)	81,962
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax		(19,000)			1,543,000	1,524,000
Net issuance of treasury stock for stock options exercised, net of shares redeemed and related tax (in shares)	8,962
Cash dividends common stock			(11,681,000)			(11,681,000)
Stock dividend equivalents restricted stock units		157,000	(157,000)
Stock-based compensation		1,017,000				1,017,000
Ending Balance at Jun. 30, 2019	$ 56,000	$ 1,246,160,000	$ (44,878,000)	$ 14,627,000	$ (12,357,000)	$ 1,203,608,000
Ending Balance (in shares) at Jun. 30, 2019	55,386,636