Securities - Securities In An Unrealized Loss Position (Details) $ in Thousands		Sep. 30, 2018 USD ($) security	Dec. 31, 2017 USD ($) security
Securities Available-for-Sale
Number of Securities | security		987
Number of Securities | security			656
Fair Value
Less Than 12 Months		$ 1,123,559
Less Than 12 Months			$ 613,975
12 Months or Longer		945,973
12 Months or Longer			1,015,438
Total		2,069,532
Total			1,629,413
Unrealized Losses
Less Than 12 Months		25,808
Less Than 12 Months			5,247
12 Months or Longer		45,947
12 Months or Longer			19,776
Total		$ 71,755
Total			$ 25,023
U.S. treasury securities
Securities Available-for-Sale
Number of Securities | security		24
Number of Securities | security			20
Fair Value
Less Than 12 Months		$ 38,623
Less Than 12 Months			$ 19,918
12 Months or Longer		10,486
12 Months or Longer			26,427
Total		49,109
Total			46,345
Unrealized Losses
Less Than 12 Months		307
Less Than 12 Months			87
12 Months or Longer		18
12 Months or Longer			97
Total		$ 325
Total			$ 184
U.S. agency securities
Securities Available-for-Sale
Number of Securities | security		75
Number of Securities | security			72
Fair Value
Less Than 12 Months		$ 81,753
Less Than 12 Months			$ 66,899
12 Months or Longer		54,161
12 Months or Longer			58,021
Total		135,914
Total			124,920
Unrealized Losses
Less Than 12 Months		1,398
Less Than 12 Months			300
12 Months or Longer		1,119
12 Months or Longer			686
Total		$ 2,517
Total			$ 986
CMOs
Securities Available-for-Sale
Number of Securities | security		260
Number of Securities | security			211
Fair Value
Less Than 12 Months		$ 610,183
Less Than 12 Months			$ 365,131
12 Months or Longer		602,362
12 Months or Longer			633,227
Total		1,212,545
Total			998,358
Unrealized Losses
Less Than 12 Months		15,445
Less Than 12 Months			3,265
12 Months or Longer		31,342
12 Months or Longer			14,689
Total		$ 46,787
Total			$ 17,954
MBSs
Securities Available-for-Sale
Number of Securities | security		119
Number of Securities | security			86
Fair Value
Less Than 12 Months		$ 215,463
Less Than 12 Months			$ 126,136
12 Months or Longer		222,989
12 Months or Longer			210,017
Total		438,452
Total			336,153
Unrealized Losses
Less Than 12 Months		5,396
Less Than 12 Months			902
12 Months or Longer		11,099
12 Months or Longer			3,432
Total		$ 16,495
Total			$ 4,334
Municipal securities
Securities Available-for-Sale
Number of Securities | security		501
Number of Securities | security			265
Fair Value
Less Than 12 Months		$ 140,916
Less Than 12 Months			$ 35,500
12 Months or Longer		55,975
12 Months or Longer			81,360
Total		196,891
Total			116,860
Unrealized Losses
Less Than 12 Months		2,762
Less Than 12 Months			479
12 Months or Longer		2,369
12 Months or Longer			781
Total		$ 5,131
Total			$ 1,260
Securities Held-to-Maturity
Number of Securities | security		8	8
Fair Value
Less Than 12 Months		$ 0	$ 0
12 Months or Longer		10,515	12,013
Total		10,515	12,013
Unrealized Losses
Less Than 12 Months		0	0
12 Months or Longer		2,158	1,747
Total		$ 2,158	$ 1,747
Corporate debt securities
Securities Available-for-Sale
Number of Securities | security		8
Fair Value
Less Than 12 Months		$ 36,621
12 Months or Longer		0
Total		36,621
Unrealized Losses
Less Than 12 Months		500
12 Months or Longer		0
Total		$ 500
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

[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."