Condensed Consolidated Statements of Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]
Beginning balance at Dec. 31, 2014	$ 878,109	$ 495,220	$ 351,814	$ 31,075
Beginning balance, shares at Dec. 31, 2014		105,893
Repurchase of common stock	(511)	$ (511)
Repurchase of common stock, shares		(33)
Exercise of stock options	4,500	$ 4,500
Exercise of stock options, shares		397
Tax benefit from exercise of stock options	742	$ 742
Shares issued pursuant to stock-based compensation plan	1,371	$ 1,371
Shares issued pursuant to stock-based compensation plan, shares		80
Cash dividends declared on common stock	(25,500)		(25,500)
Net earnings	42,646		42,646
Other comprehensive income (loss)	(7,366)			(7,366)
Ending balance at Jun. 30, 2015	893,991	$ 501,322	368,960	23,709
Ending balance, shares at Jun. 30, 2015		106,337
Beginning balance at Dec. 31, 2015	923,399	$ 502,571	399,919	20,909
Beginning balance, shares at Dec. 31, 2015		106,385
Repurchase of common stock	(408)	$ (408)
Repurchase of common stock, shares		(40)
Issuance of common stock for acquisition of County Commerce Bank	21,642	$ 21,642
Issuance of common stock for acquisition of County Commerce Bank, Shares		1,394
Exercise of stock options	2,254	$ 2,254
Exercise of stock options, shares		175
Tax benefit from exercise of stock options	86	$ 86
Shares issued pursuant to stock-based compensation plan	1,307	$ 1,307
Shares issued pursuant to stock-based compensation plan, shares		33
Cash dividends declared on common stock	(25,885)		(25,885)
Net earnings	48,905		48,905
Other comprehensive income (loss)	20,163			20,163
Ending balance at Jun. 30, 2016	$ 991,463	$ 527,452	$ 422,939	$ 41,072
Ending balance, shares at Jun. 30, 2016		107,947