Fair Value (Financial Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands		Jun. 30, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		$ 2,308,812	$ 2,093,404
Derivative assets	[1]	43,903	23,251
Total recurring fair value measurements - assets		2,352,715	2,116,655
Derivative liabilities	[1]	43,184	23,968
Total recurring fair value measurements - liabilities		43,184	23,968
US Treasury and Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		116	134
Municipal Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		156,292	39,607
Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		3,500	3,500
Mortgage-Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		1,906,346	1,758,373
Collateralized Mortgage Obligations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		241,346	289,033
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		1,212	2,757
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		1,212	2,757
Total recurring fair value measurements - assets		1,212	2,757
Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		2,307,600	2,090,647
Derivative assets	[1]	43,903	23,251
Total recurring fair value measurements - assets		2,351,503	2,113,898
Derivative liabilities	[1]	43,184	23,968
Total recurring fair value measurements - liabilities		43,184	23,968
Recurring [Member] | US Treasury and Government Agency Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		116	134
Recurring [Member] | Municipal Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		156,292	39,607
Recurring [Member] | Corporate Debt Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		3,500	3,500
Recurring [Member] | Mortgage-Backed Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		1,906,346	1,758,373
Recurring [Member] | Collateralized Mortgage Obligations [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		241,346	289,033
Recurring [Member] | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for sale securities		$ 1,212	$ 2,757

[1] For further disaggregation of derivative assets and liabilities, see Note 6 - Derivatives.