Securities - Securities In An Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Securities Available-for-Sale
Number of Securities | security	313	882
Fair Value
Less Than 12 Months	$ 43,047	$ 501,061
12 Months or Longer	770,455	1,365,068
Total	813,502	1,866,129
Unrealized Losses
Less Than 12 Months	138	8,046
12 Months or Longer	7,126	36,270
Total	$ 7,264	$ 44,316
U.S. treasury securities
Securities Available-for-Sale
Number of Securities | security	5	17
Fair Value
Less Than 12 Months	$ 0	$ 15,894
12 Months or Longer	13,982	13,886
Total	13,982	29,780
Unrealized Losses
Less Than 12 Months	0	57
12 Months or Longer	21	118
Total	$ 21	$ 175
U.S. agency securities
Securities Available-for-Sale
Number of Securities | security	51	74
Fair Value
Less Than 12 Months	$ 186	$ 34,263
12 Months or Longer	82,022	93,227
Total	82,208	127,490
Unrealized Losses
Less Than 12 Months	7	320
12 Months or Longer	653	1,287
Total	$ 660	$ 1,607
CMOs
Securities Available-for-Sale
Number of Securities | security	108	234
Fair Value
Less Than 12 Months	$ 9,896	$ 171,901
12 Months or Longer	371,269	863,747
Total	381,165	1,035,648
Unrealized Losses
Less Than 12 Months	31	1,671
12 Months or Longer	2,650	23,013
Total	$ 2,681	$ 24,684
MBSs
Securities Available-for-Sale
Number of Securities | security	83	118
Fair Value
Less Than 12 Months	$ 21,325	$ 135,791
12 Months or Longer	250,402	284,273
Total	271,727	420,064
Unrealized Losses
Less Than 12 Months	71	1,715
12 Months or Longer	2,744	9,536
Total	$ 2,815	$ 11,251
Municipal securities
Securities Available-for-Sale
Number of Securities | security	57	423
Fair Value
Less Than 12 Months	$ 608	$ 60,863
12 Months or Longer	23,646	109,935
Total	24,254	170,798
Unrealized Losses
Less Than 12 Months	8	558
12 Months or Longer	98	2,316
Total	$ 106	$ 2,874
Securities Held-to-Maturity
Number of Securities | security	32	5
Fair Value
Less Than 12 Months	$ 12,884	$ 0
12 Months or Longer	9,521	9,871
Total	22,405	9,871
Unrealized Losses
Less Than 12 Months	501	0
12 Months or Longer	371	305
Total	$ 872	$ 305
Corporate debt securities
Securities Available-for-Sale
Number of Securities | security	9	16
Fair Value
Less Than 12 Months	$ 11,032	$ 82,349
12 Months or Longer	29,134	0
Total	40,166	82,349
Unrealized Losses
Less Than 12 Months	21	3,725
12 Months or Longer	960	0
Total	$ 981	$ 3,725