Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income	$ 52,503	$ 47,834	$ 102,225	$ 98,263
Total available-for-sale and transferred securities	(13,927)	15,751	(6,960)	23,873
Total derivative instruments	2,331	(2,518)	561	(6,244)
Total defined benefit pension and other postretirement benefit plans	991	463	1,965	925
Other comprehensive (loss) income, net of tax	(10,605)	13,696	(4,434)	18,554
Comprehensive income	$ 41,898	$ 61,530	$ 97,791	$ 116,817