Significant Accounting Policies - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of cash flows specific transaction amounts [Abstract]
Income taxes paid		$ 7,371	$ 24,836	$ 16,321
Interest expense paid on deposits and borrowings		41,472	24,312	20,733
Noncash transfers from loans to other real estate	[1]	8,760	23,965	$ 32,782
Transfer of long-term FHLB advances to short-term		250,038	$ 500,009
Assets acquired in business combination		196,265
Liabilities assumed in business combination		$ 184,949

[1] Includes transfers from covered loans to foreclosed properties.