CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income	$ 30,506	$ 24,414
Other comprehensive (loss) income, net of tax
Unrealized gains (losses) on investment securities arising during the period	(9,830)	1,487
Change in retirement obligation	323	189
Unrealized gain (loss) on derivatives	156	128
Other comprehensive income (loss)	(9,351)	1,804
Comprehensive income	$ 21,155	$ 26,218