CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 36,418	$ 22,736	$ 66,924	$ 47,150
Other comprehensive (loss) income, net of tax
Unrealized gain (loss) on investment securities arising during the period	(8,978)	4,076	(18,808)	5,563
Change in retirement obligation	494	213	817	402
Unrealized gain (loss) on derivatives	159	128	315	256
Other comprehensive income (loss)	(8,325)	4,417	(17,676)	6,221
Comprehensive income	$ 28,093	$ 27,153	$ 49,248	$ 53,371