Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]
Balance at Dec. 31, 2013	$ 2,186,722	$ 3	$ 239,986	$ (101)	$ 1,606,117	$ 340,717
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	88,845				88,845
Other comprehensive income, net of tax						(121,772)
Issuance of common stock	15,051		15,051
Stock compensation expense			14,888
Tax benefit-exercise stock options			1,421
Balance at Dec. 31, 2014	2,185,155	3	271,346	(101)	1,694,962	218,945
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	113,093				113,093
Other comprehensive income, net of tax						163,193
Issuance of common stock	8,236		8,236
Stock compensation expense			16,983
Tax benefit-exercise stock options			3,843
Balance at Dec. 31, 2015	2,490,503	3	300,408	(101)	1,808,055	382,138
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	28,125				28,125
Other comprehensive income, net of tax						35,628
Issuance of common stock	11,280		11,280
Stock compensation expense			19,730
Tax benefit-exercise stock options			1,493
Balance at Dec. 31, 2016	$ 2,586,759	$ 3	$ 332,911	$ (101)	$ 1,836,180	$ 417,766