Parent Company Financial Information (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Assets
Investment securities available-for-sale, at fair value	$ 589,268	$ 538,108
Other assets	71,784	52,653
Total Assets	7,479,029	6,890,096
Liabilities
Other liabilities	56,141	45,793
Long-term borrowings	216,905	216,514	$ 70,000
Total Liabilities	6,528,591	6,047,297
Shareholders' Equity
Common stock	340	338
Additional paid in capital	520,304	513,531
Retained earnings	431,544	331,311
Accumulated other comprehensive income (loss)	(1,750)	(2,381)	191	$ 2,647
Total Shareholders' Equity	950,438	842,799	$ 738,601	$ 620,759
Total Liabilities and Shareholders' Equity	7,479,029	6,890,096
Parent Company [Member]
Assets
Cash	77,883	86,561
Investment securities available-for-sale, at fair value	100	100
Investment in subsidiaries	1,088,670	973,530
Other assets	5,315	3,935
Total Assets	1,171,968	1,064,126
Liabilities
Other liabilities	4,625	4,813
Long-term borrowings	216,905	216,514
Total Liabilities	221,530	221,327
Shareholders' Equity
Common stock	340	338
Additional paid in capital	520,304	513,531
Retained earnings	431,544	331,311
Accumulated other comprehensive income (loss)	(1,750)	(2,381)
Total Shareholders' Equity	950,438	842,799
Total Liabilities and Shareholders' Equity	$ 1,171,968	$ 1,064,126