Fair Value Measurements - Carrying Amounts and Estimated Fair Values of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Level 1 | Carrying Amount
Financial Assets:
Cash and cash equivalents	$ 414,919	$ 316,705
Level 1 | Estimated Fair Value
Financial Assets:
Cash and cash equivalents	414,919	316,705
Level 2 | Carrying Amount
Financial Assets:
Loans held for sale	53,324	44,115
Customers' liabilities on acceptances	5,719	5,602
Financial Liabilities:
Noninterest-bearing deposits	1,512,423	1,399,454
Saving and other interest bearing demand deposits	1,653,561	1,598,514
Time deposits	2,304,404	2,150,089
FHLB advances	461,166	421,352
Subordinated debentures	42,076	57,410
Bank's liabilities on acceptances outstanding	5,719	5,602
Level 2 | Estimated Fair Value
Financial Assets:
Loans held for sale	55,990	45,975
Customers' liabilities on acceptances	5,719	5,602
Financial Liabilities:
Noninterest-bearing deposits	1,512,423	1,399,454
Saving and other interest bearing demand deposits	1,653,561	1,598,514
Time deposits	2,311,628	2,156,514
FHLB advances	462,121	421,258
Subordinated debentures	43,998	56,544
Bank's liabilities on acceptances outstanding	5,719	5,602
Level 3 | Carrying Amount
Financial Assets:
Loans receivable - net	5,280,187	5,006,856
FDIC loss share receivable	0	1,110
Level 3 | Estimated Fair Value
Financial Assets:
Loans receivable - net	5,661,842	5,450,008
FDIC loss share receivable	$ 0	$ 1,110