CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 22,736	$ 22,568	$ 47,150	$ 42,382
Other comprehensive (loss) income, net of tax
Unrealized gains (losses) on investment securities arising during the period	4,076	5,192	5,563	12,235
Change in retirement obligation	213	201	402	401
Unrealized gain (loss) on derivatives	128	128	256	256
Other comprehensive income (loss)	4,417	5,521	6,221	12,892
Comprehensive income	$ 27,153	$ 28,089	$ 53,371	$ 55,274