Debt Securities Available for Sale - Continuous Unrealized Loss Position of Available-for-Sale Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	$ 38,954	$ 217,762
Less than 12 months, gross unrealized (losses)	(366)	(1,748)
12 months or longer, fair value	232,026	552,442
12 months or longer, gross unrealized (losses)	(2,572)	(18,310)
Fair value	270,980	770,204
Gross unrealized (losses)	(2,938)	(20,058)
U.S. government and agency obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	0	14,668
Less than 12 months, gross unrealized (losses)	0	(202)
12 months or longer, fair value	19,928	29,437
12 months or longer, gross unrealized (losses)	(46)	(515)
Fair value	19,928	44,105
Gross unrealized (losses)	(46)	(717)
Mortgage-backed securities and collateralized mortgage obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	29,160	176,614
Less than 12 months, gross unrealized (losses)	(158)	(1,034)
12 months or longer, fair value	193,169	509,397
12 months or longer, gross unrealized (losses)	(1,455)	(16,402)
Fair value	222,329	686,011
Gross unrealized (losses)	(1,613)	(17,436)
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	9,794	26,480
Less than 12 months, gross unrealized (losses)	(208)	(512)
12 months or longer, fair value	14,422	9,358
12 months or longer, gross unrealized (losses)	(578)	(643)
Fair value	24,216	35,838
Gross unrealized (losses)	(786)	(1,155)
Trust preferred securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	0	0
Less than 12 months, gross unrealized (losses)	0	0
12 months or longer, fair value	4,507	4,250
12 months or longer, gross unrealized (losses)	(493)	(750)
Fair value	4,507	4,250
Gross unrealized (losses)	$ (493)	$ (750)