Fair Value Measurements on a Recurring Basis (Details) - Recurring Measurements - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Financial Assets
Total assets measured at fair value on a recurring basis	$ 2,292,079	$ 2,610,760
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	26,526	19,499
Interest rate swaps
Financial Liabilities
Interest rate swaps	26,526	19,499
U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	41,593	47,451
U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	16,367	93,167
State and local governments
Financial Assets
Investment securities, available-for-sale	852,059	885,019
Corporate bonds
Financial Assets
Investment securities, available-for-sale	404,413	384,163
Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	977,647	1,200,960
Level 1
Financial Assets
Total assets measured at fair value on a recurring basis	0	0
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	0	0
Level 1 | Interest rate swaps
Financial Liabilities
Interest rate swaps	0	0
Level 1 | U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 | U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 | State and local governments
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 | Corporate bonds
Financial Assets
Investment securities, available-for-sale	0	0
Level 1 | Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	0	0
Level 2
Financial Assets
Total assets measured at fair value on a recurring basis	2,292,079	2,610,760
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	26,526	19,499
Level 2 | Interest rate swaps
Financial Liabilities
Interest rate swaps	26,526	19,499
Level 2 | U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	41,593	47,451
Level 2 | U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	16,367	93,167
Level 2 | State and local governments
Financial Assets
Investment securities, available-for-sale	852,059	885,019
Level 2 | Corporate bonds
Financial Assets
Investment securities, available-for-sale	404,413	384,163
Level 2 | Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	977,647	1,200,960
Level 3
Financial Assets
Total assets measured at fair value on a recurring basis	0	0
Financial Liabilities
Total liabilities measured at fair value on a recurring basis	0	0
Level 3 | Interest rate swaps
Financial Liabilities
Interest rate swaps	0	0
Level 3 | U.S. government and federal agency
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 | U.S. government sponsored enterprises
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 | State and local governments
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 | Corporate bonds
Financial Assets
Investment securities, available-for-sale	0	0
Level 3 | Residential mortgage-backed securities
Financial Assets
Investment securities, available-for-sale	$ 0	$ 0