Securities - Securities In An Unrealized Loss Position (Details) $ in Thousands		Mar. 31, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Securities Available-for-Sale
Number of Securities | security		885	656
Fair Value
Less Than 12 Months		$ 900,386	$ 613,975
12 Months or Longer		1,015,084	1,015,438
Total		1,915,470	1,629,413
Unrealized Losses
Less Than 12 Months		15,081	5,247
12 Months or Longer		34,343	19,776
Total		$ 49,424	$ 25,023
U.S. treasury securities
Securities Available-for-Sale
Number of Securities | security		22	20
Fair Value
Less Than 12 Months		$ 32,744	$ 19,918
12 Months or Longer		60,664	26,427
Total		93,408	46,345
Unrealized Losses
Less Than 12 Months		222	87
12 Months or Longer		74	97
Total		$ 296	$ 184
U.S. agency securities
Securities Available-for-Sale
Number of Securities | security		77	72
Fair Value
Less Than 12 Months		$ 69,433	$ 66,899
12 Months or Longer		17,446	58,021
Total		86,879	124,920
Unrealized Losses
Less Than 12 Months		519	300
12 Months or Longer		1,025	686
Total		$ 1,544	$ 986
CMOs
Securities Available-for-Sale
Number of Securities | security		238	211
Fair Value
Less Than 12 Months		$ 524,167	$ 365,131
12 Months or Longer		621,039	633,227
Total		1,145,206	998,358
Unrealized Losses
Less Than 12 Months		9,432	3,265
12 Months or Longer		22,776	14,689
Total		$ 32,208	$ 17,954
MBSs
Securities Available-for-Sale
Number of Securities | security		98	86
Fair Value
Less Than 12 Months		$ 190,166	$ 126,136
12 Months or Longer		212,297	210,017
Total		402,463	336,153
Unrealized Losses
Less Than 12 Months		3,677	902
12 Months or Longer		7,637	3,432
Total		$ 11,314	$ 4,334
Municipal securities
Securities Available-for-Sale
Number of Securities | security		447	265
Fair Value
Less Than 12 Months		$ 74,891	$ 35,500
12 Months or Longer		103,638	81,360
Total		178,529	116,860
Unrealized Losses
Less Than 12 Months		1,210	479
12 Months or Longer		2,831	781
Total		$ 4,041	$ 1,260
Corporate debt securities
Securities Available-for-Sale
Number of Securities | security		3
Fair Value
Less Than 12 Months		$ 8,985
12 Months or Longer		0
Total		8,985
Unrealized Losses
Less Than 12 Months		21
12 Months or Longer		0
Total		$ 21
Equity securities
Securities Available-for-Sale
Number of Securities | security	[1]		2
Fair Value
Less Than 12 Months	[1]		$ 391
12 Months or Longer	[1]		6,386
Total	[1]		6,777
Unrealized Losses
Less Than 12 Months	[1]		214
12 Months or Longer	[1]		91
Total	[1]		$ 305
Municipal securities
Securities Held-to-Maturity
Number of Securities | security		8	8
Fair Value
Less Than 12 Months		$ 0	$ 0
12 Months or Longer		11,287	12,013
Total		11,287	12,013
Unrealized Losses
Less Than 12 Months		0	0
12 Months or Longer		2,113	1,747
Total		$ 2,113	$ 1,747

[1] (1) As a result of accounting guidance adopted in the first quarter of 2018, equity securities are no longer presented within securities available-for-sale and are now presented within equity securities in the Consolidated Statements of Financial Condition for the current period. For further discussion of this guidance, see Note 2, "Recent Accounting Pronouncements."