CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net change in unrealized gains on available-for-sale securities, tax effect	$ 2,666	$ 247
Net change in unrealized gains (losses) on cash flow hedging derivatives, tax effect	355	48
Net reclassification adjustment for effective portion of cash flow hedges included in interest expense, tax effect	(13)	(159)
Reclassification of amortization of prior service cost included in net periodic cost, tax effect	$ (31)	$ (23)